Magnetic field sensor integrated circuit with integral ferromagnetic material

ABSTRACT

A magnetic field sensor includes a lead frame, a semiconductor die having a first surface in which a magnetic field sensing element is disposed and a second surface attached to the lead frame, and a non-conductive mold material enclosing the die and at least a portion of the lead frame. The sensor may include a ferromagnetic mold material secured to a portion of the non-conductive mold material. Features include a multi-sloped taper to an inner surface of a non-contiguous central region of the ferromagnetic mold material, a separately formed element disposed in the non-contiguous central region, one or more slots in the lead frame, a molded ferromagnetic suppression device spaced from the non-conductive mold material and enclosing a portion of a lead, a passive device spaced from the non-conductive mold material and coupled to a plurality of leads, and a ferromagnetic bead coupled to a lead. Also described is a coil secured to the non-conductive mold material and a lead having at least two separated portions with a passive component coupled across the two portions.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a Continuation-in-Part application and claims thebenefit of U.S. patent application Ser. No. 13/424,618, filed on Mar.20, 2012, which is incorporated herein by reference in its entirety.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH

Not Applicable.

FIELD OF THE INVENTION

This invention relates generally to magnetic field sensors and, moreparticularly, to integrated circuit magnetic field sensors having anintegral ferromagnetic material.

BACKGROUND OF THE INVENTION

Magnetic field sensors including a magnetic field sensing element, ortransducer, such as a Hall Effect element or a magnetoresistive element,are used in a variety of applications to detect aspects of movement of aferromagnetic article, or target, such as proximity, speed, anddirection. Illustrative applications include, but are not limited to, amagnetic switch or “proximity detector” that senses the proximity of aferromagnetic article, a proximity detector that senses passingferromagnetic articles (for example, magnetic domains of a ring magnetor gear teeth), a magnetic field sensor that senses a magnetic fielddensity of a magnetic field, and a current sensor that senses a magneticfield generated by a current flowing in a current conductor. Magneticfield sensors are widely used in automobile control systems, forexample, to detect ignition timing from a position of an enginecrankshaft and/or camshaft, and to detect a position and/or rotation ofan automobile wheel for anti-lock braking systems.

In applications in which the ferromagnetic target is magnetic, amagnetically permeable concentrator or magnetic flux guide is sometimesused to focus the magnetic field generated by the target on the magneticfield transducer, thus increasing the sensitivity of the sensor,allowing the use of a smaller magnetic target, and/or allowing themagnetic target to be sensed from a larger distance (i.e., a largerairgap). In other applications, in which the ferromagnetic target is notmagnetic, a permanent magnet, sometimes referred to as a back biasmagnet, may be used to generate the magnetic field that is then alteredby movement of the target.

In some applications it is desirable to provide a back bias magnet withtwo magnetic poles on the magnet surface adjacent to the magnetic fieldtransducer. For example, as described in a U.S. Pat. No. 5,781,005entitled “Hall-Effect Ferromagnetic-Article-Proximity Sensor,” which isassigned to the Assignee of the subject application, the near presenceof opposite poles serves to short out the lines of flux when noferromagnetic article is present, thereby presenting a significant andeasily recognizable difference between an article present (e.g., geartooth present) condition and an article absent (e.g., gear valleypresent) condition and maintaining a low magnetic flux density baselineregardless of airgap. Because of the easily recognizable difference inthe magnetic field signal, these types of arrangements are advantageousfor use in sensors in which it is necessary to detect thepresence/absence of a magnetic article, such sensors sometimes beingreferred to as True Power On Sensors, or TPOS, sensors.

Generally, back bias magnets and concentrators are held in placerelative to the magnetic field sensing element by mechanical means, suchas an adhesive as shown in a U.S. Pat. No. 6,265,865 entitled “SingleUnitary Plastic Package for a Magnetic Field Sensing Device,” which isassigned to the Assignee of the subject application. Such mechanicalpositioning can lead to performance variations, such as sensitivityvariations, from device to device due to position tolerances. Thus, itis advantageous to manufacture the sensor so that the sensor and theback bias magnet or concentrator are integrally formed, therebyeliminating position tolerances. A magnetic field sensor of this type isdescribed in a U.S. Patent Application Publication No. 2010/0141249entitled “Magnetic Field Sensors and Methods for Fabricating theMagnetic Field Sensors,” which is also assigned to the Assignee of thesubject application and in which a concentrator or magnet may be formedby a liquid encapsulant or a combination of a liquid encapsulant andpermanent magnet in a cavity on the side of the sensor opposite thetarget.

While the use of a back bias magnet is advantageous in certainapplications, the hard magnetic material used to form the magnet isrelatively expensive and represents a significant part of the overallcost of the sensor.

There are many package types and fabrication techniques in use forproviding integrated circuit magnetic field sensors. For example, thesemiconductor die in which the magnetic field sensing element is formedmay be attached to a lead frame by various techniques, such as with anadhesive tape or epoxy, and may be electrically coupled to the leadframe by various techniques, such as with solder bumps or wire bonding.Also, the lead frame may take various forms and the semiconductor diemay be attached to the lead frame in an orientation with the activesemiconductor surface (i.e., the surface in which the magnetic fieldsensing element is formed) being adjacent to the lead frame in a socalled “flip-chip” arrangement, with the active semiconductor surfaceopposite the lead frame surface in a so called “die up” arrangement, orwith the semiconductor die positioned below the lead frame in a socalled “Lead on Chip” arrangement.

Molding is often used in fabricating integrated circuit magnetic fieldsensors to provide the protective and electrically insulative “overmold”to the semiconductor die. Transfer molding has also been used to formtwo different molded portions for various reasons. For example, in aU.S. Pat. No. 7,816,772 entitled “Methods and Apparatus for Multi-StageMolding of Integrated Circuit Package” which is assigned to the Assigneeof the subject application, a first molded structure is formed over thesemiconductor die to protect wire bonds and the device is overmoldedwith a second molded structure formed over the first molded structure.In a U.S. Patent Application Publication No. 2009/0140725 entitled“Integrated Circuit Including Sensor having Injection Molded MagneticMaterial,” an injection molded magnetic material encloses at least aportion of a magnetic field sensor.

Molding, while providing a cost effective fabrication technique, canpresent challenges, such as removal of the device from the mold in amanner that does not subject the device to deleterious stresses.

SUMMARY OF THE INVENTION

A magnetic field sensor includes a lead frame having a first surface anda second opposing surface, a semiconductor die having a first surface inwhich a magnetic field sensing element is disposed and a second opposingsurface attached to the first surface of the lead frame, anon-conductive mold material enclosing the die and at least a portion ofthe lead frame, and a ferromagnetic mold material secured to a portionof the non-conductive mold material, wherein the ferromagnetic moldmaterial comprises a non-contiguous central region extending from afirst end proximate to the lead frame to a second end distal from thelead frame, wherein the central region has an inner surface with a taperestablished by at least two differently sloped portions.

The ferromagnetic mold material is secured to a portion of thenon-conductive mold material and a second portion of the lead frame thatextends beyond the non-conductive mold material and may comprise a hardferromagnetic material. A third mold material may be disposed in andsecured to the central region of the ferromagnetic mold material. Insome embodiments, a separately formed element, as may be comprised of ahard ferromagnetic material, a soft ferromagnetic material, or anon-ferromagnetic material, is disposed in and secured to the centralregion of the ferromagnetic mold material.

Also described is a magnetic field sensor including a lead frame havinga first surface and a second opposing surface, a semiconductor diehaving a first surface in which a magnetic field sensing element isdisposed and a second opposing surface attached to the first surface ofthe lead frame, a non-conductive mold material enclosing the die and atleast a portion of the lead frame, a ferromagnetic mold material securedto a portion of the non-conductive mold material, wherein theferromagnetic mold material comprises a non-contiguous central regionextending from a first end proximate to the lead frame to a second enddistal from the lead frame, and a separately formed element disposed inand secured to the central region of the ferromagnetic mold material.The separately formed element may be comprised of a hard ferromagneticmaterial, a soft ferromagnetic material, or a non-ferromagneticmaterial. In some embodiments, the lead frame may include at least oneslot.

According to a further aspect, a magnetic field sensor includes a leadframe having a first surface, a second opposing surface, and at leastone slot, a semiconductor die having a first surface in which a magneticfield sensing element is disposed and a second opposing surface attachedto the first surface of the lead frame, a non-conductive mold materialenclosing the die and at least a portion of the lead frame, and aferromagnetic mold material secured to a portion of the non-conductivemold material. In some embodiments, the ferromagnetic mold materialcomprises a hard ferromagnetic material to form a bias magnet.

Also described is a magnetic field sensor including a lead frame havinga first surface, a second opposing surface, and a plurality of leads, asemiconductor die having a first surface in which a magnetic fieldsensing element is disposed and a second opposing surface attached tothe first surface of the lead frame, a non-conductive mold materialenclosing the die and at least a portion of the lead frame, and a moldedferromagnetic suppression device spaced from the non-conductive moldmaterial and enclosing a portion of at least one of the plurality ofleads. A ferromagnetic mold material may be secured to a portion of thenon-conductive mold material. The molded ferromagnetic suppressiondevice may comprise comprises a hard ferromagnetic material or a softferromagnetic material.

In some embodiments, the molded ferromagnetic suppression deviceincludes a first molded element enclosing the portion of a lead and asecond molded element enclosing at least a portion of the first moldedelement. The first molded element may comprise a non-conductive moldmaterial and the second molded element may comprise a ferromagneticmaterial. According to a further aspect, the sensor may include at leastone of a passive component or a ferromagnetic bead coupled to a lead andenclosed by the molded ferromagnetic suppression device.

Also described is a magnetic field sensor including a lead frame havinga first surface, a second opposing surface, and a plurality of leads, asemiconductor die having a first surface in which a magnetic fieldsensing element is disposed and a second opposing surface, anon-conductive mold material enclosing the die and at least a portion ofthe lead frame, a ferromagnetic mold material secured to a portion ofthe non-conductive mold material, and at least one capacitor coupled toat least two of the plurality of leads and spaced from thenon-conductive mold material. Additional features may include a moldedferromagnetic suppression device enclosing the capacitor, at least oneslot in the lead frame, and/or at least one ferromagnetic bead coupledto a lead.

According to a further aspect, a magnetic field sensor includes a leadframe having a first surface, a second opposing surface, and a pluralityof leads, a semiconductor die having a first surface in which a magneticfield sensing element is disposed and a second opposing surface, anon-conductive mold material enclosing the die and at least a portion ofthe lead frame, a ferromagnetic mold material secured to a portion ofthe non-conductive mold material, and at least one ferromagnetic beadcoupled to at least one of the plurality of leads. In some embodiments,the ferromagnetic bead is enclosed by the non-conductive mold material.A molded ferromagnetic suppression device may be provided spaced fromthe non-conductive mold material and may enclose the ferromagnetic bead.

Also described is a magnetic field sensor including a lead frame havinga first surface and a second opposing surface, a semiconductor diehaving a first surface in which a magnetic field sensing element isdisposed and a second opposing surface attached to the first surface ofthe lead frame, a non-conductive mold material enclosing the die and atleast a portion of the lead frame, and a conductive coil secured to thenon-conductive mold material. In some embodiments, the non-conductivemold material encloses the coil. Alternatively, a second mold materialmay be secured to a portion of the non-conductive mold material andenclose the coil. The non-conductive mold material may include aprotrusion and the coil may be positioned concentrically with respect tothe protrusion.

Also described is a magnetic field sensor including a lead frame havinga first surface, a second opposing surface, and at least one leadcomprising a first lead portion having an end and a second lead portionhaving an end spaced from and proximate to the end of the first leadportion, a semiconductor die having a first surface in which a magneticfield sensing element is disposed and a second opposing surface attachedto the first surface of the lead frame, a non-conductive mold materialenclosing the die and at least a portion of the lead frame, and apassive component coupled between the end of the first lead portion andthe end of the second lead portion. In some embodiments, the passivecomponent is a resistor.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing features of the invention, as well as the invention itselfmay be more fully understood from the following detailed description ofthe drawings, in which:

FIG. 1 is a cross-sectional view of a magnetic field sensor having anon-conductive mold material and a ferromagnetic mold material and asecuring mechanism between the non-conductive and ferromagnetic moldmaterials;

FIG. 1A is a cross-sectional view of the sensor of FIG. 1 taken alongline A-A of FIG. 1;

FIG. 1B is a cross-sectional view of the sensor of FIG. 1 taken alongline B-B of FIG. 1;

FIG. 1C is an alternative cross-sectional view of the sensor of FIG. 1taken along line B-B of FIG. 1 and illustrating an alternative securingmechanism;

FIG. 2 is a cross-sectional view of the magnetic field sensor of FIG. 1further having a third mold material and illustrating a furtheralternative securing mechanism;

FIG. 2A is a cross-sectional view of an alternative magnetic fieldsensor having the third mold material and alternative securing mechanismas shown in FIG. 2;

FIG. 3 is a cross-sectional view of an alternative packaged magneticfield sensor having a non-conductive mold material, a ferromagnetic moldmaterial, and a third mold material;

FIG. 3A is a cross-sectional view of another alternative packagedmagnetic field sensor having a non-conductive mold material, and aferromagnetic mold material, and a third mold material;

FIG. 4 is a plan view of a packaged magnetic field sensor havingintegrated components coupled to the lead frame, a non-conductive moldmaterial, and a ferromagnetic mold material;

FIG. 4A is a cross-sectional view of the sensor of FIG. 4 taken alongline A-A of FIG. 4;

FIG. 5 is a plan view of a surface mount packaged magnetic field sensorhaving integrated components coupled to the opposite side of the leadframe from the die, a non-conductive mold material, and a ferromagneticmold material;

FIG. 5A is a cross-sectional view of the sensor of FIG. 5 taken alongline A-A of FIG. 5;

FIG. 5B is an alternative cross-sectional view of the sensor of FIG. 5taken along line A-A of FIG. 5;

FIG. 6 is a perspective view of a flip-chip surface mount packagedmagnetic field sensor having an integrated component coupled to theopposite side of the lead frame from the die, a non-conductive moldmaterial, and a ferromagnetic mold material;

FIG. 7 is a cross-sectional view of a magnetic field sensor having aplurality of magnetic field sensing elements, a non-conductive moldmaterial, and a ferromagnetic mold material;

FIG. 8 is a flow diagram illustrating an exemplary process forfabricating the magnetic field sensors of FIGS. 1-7;

FIG. 8A is a flow diagram illustrating an alternative process forfabricating the magnetic field sensors of FIGS. 1-7;

FIG. 9 shows a semiconductor wafer having a ferromagnetic material layeraccording to a further aspect;

FIG. 10 shows a packaged magnetic field sensor formed from the wafer ofFIG. 9;

FIG. 11 is a perspective view of a magnetic field sensor formed from thewafer of FIG. 9 and having solder bumps suitable for certain integratedcircuit packaging options;

FIG. 12 is a cross-sectional view of an alternative magnetic fieldsensor formed from the wafer of FIG. 9 and having solder bumps;

FIG. 13 is yet another alternative magnetic field sensor formed with thewafer of FIG. 9 and having solder bumps;

FIG. 14 is a flow diagram illustrating an exemplary process forfabricating the magnetic field sensors of FIGS. 10-13;

FIG. 15 is a magnetic field sensor according to a further aspect;

FIG. 16 is a flow diagram illustrating an exemplary process forfabricating the magnetic field sensor of FIG. 15;

FIG. 17 is a plan view of an alternative packaged magnetic field sensor;

FIG. 18 is a cross-sectional view of an alternative magnetic fieldsensor having a central aperture surface with a dual-sloped taper;

FIG. 19 is a cross-sectional view of yet another alternative magneticfield sensor having a separately formed element in the central aperture;

FIG. 20 is a plan view of an alternative magnetic field sensor havingslots in the lead frame and a passive device in series with a lead;

FIG. 21 is a side cross-sectional view of a magnetic field sensor havinga non-conductive mold material, a ferromagnetic mold material, andmolded ferromagnetic suppression device enclosing a portion of a lead;

FIG. 21A plan view of the magnetic field sensor of FIG. 21;

FIG. 21B is a plan view of the magnetic field sensor of FIG. 21 showingan alternative molded ferromagnetic suppression device;

FIG. 22 is a side cross-sectional view of a magnetic field sensor havinga non-conductive mold material, a ferromagnetic mold material, and analternative molded ferromagnetic suppression device enclosing a portionof a lead;

FIG. 23 is a side cross-sectional view of a magnetic field sensor havinga non-conductive mold material, a ferromagnetic mold material, andmolded ferromagnetic suppression device enclosing a passive componentand a portion of a lead;

FIG. 23A is a plan view of the magnetic field sensor of FIG. 23;

FIG. 23B is a plan view of the magnetic field sensor of FIG. 23 showingan alternative arrangement for the passive components relative to theleads;

FIG. 24 is side a cross-sectional view of an alternative magnetic fieldsensor having a non-conductive mold material, a ferromagnetic moldmaterial, and molded ferromagnetic suppression device enclosing apassive component and a portion of a lead;

FIG. 25 is a side cross-sectional view of a magnetic field sensor havinga non-conductive mold material, a ferromagnetic mold material, andmolded ferromagnetic suppression device enclosing a ferrite bead and aportion of a lead;

FIG. 26 is a side cross-sectional view of a magnetic field sensor havinga non-conductive mold material, a ferromagnetic mold material, andmolded ferromagnetic suppression device enclosing a passive component, aferrite bead, and a portion of a lead;

FIG. 26A is a plan view the magnetic field sensor of FIG. 26;

FIG. 27 is a cross-sectional view of a magnetic field sensor having anon-conductive mold material, a coil, and a ferromagnetic mold material;

FIG. 28 is a cross-sectional view of an alternative magnetic fieldsensor having a non-conductive mold material, a coil, and aferromagnetic mold material; and

FIG. 29 is a cross-sectional view of another alternative magnetic fieldsensor having a non-conductive mold material and a coil.

DETAILED DESCRIPTION OF THE INVENTION

Referring to the cross-sectional view of FIG. 1, and also to thecross-sectional views of FIGS. 1A and 1B, a magnetic field sensor 10includes a semiconductor die 14 having a first, active surface 14 a inwhich a magnetic field sensing element or transducer 22 is formed and asecond, opposing surface 14 b attached to a die attach area 16 on afirst surface 18 a of a lead frame 18, a non-conductive mold material 20enclosing the die and at least a portion of the lead frame, and aferromagnetic mold material 30 secured to the non-conductive moldmaterial. The ferromagnetic mold material 30 comprises a ferromagneticmaterial and is tapered from a first end 30 a proximate to the leadframe 18 to a second end 30 b distal from the lead frame. The active diesurface 14 a is opposite the die surface 14 b which is attached to thedie attach area 16 and thus, this configuration may be referred to as a“die up” arrangement.

The magnetic field sensing element 22 in this and other embodiments canbe, but is not limited to, a Hall effect element, a magnetoresistanceelement, or a magnetotransistor. As is known, there are different typesof Hall effect elements, for example, a planar Hall element, a verticalHall element, and a circular vertical Hall element. As is also known,there are different types of magnetoresistance elements, for example, asemiconductor magnetoresistance element such as Indium Antimonide(InSb), a giant magnetoresistance (GMR) element, an anisotropicmagnetoresistance element (AMR), a tunneling magnetoresistance (TMR)element, and a magnetic tunnel junction (MTJ). The sensing element 22may include a single element or, alternatively, may include two or moreelements arranged in various configurations, e.g., a half bridge or full(Wheatstone) bridge. The sensing element 22 may be a device made of atype IV semiconductor material such as Silicon (Si) or Germanium (Ge),or a type III-V semiconductor material like Gallium-Arsenide (GaAs) oran Indium compound, e.g., Indium-Antimonide (InSb). In some embodiments,it may be desirable to use two or more substrates, one for the magneticfield sensing element(s) and another, such as a Si substrate, forassociated processing circuitry. Illustrative multiple substratearrangements are described in U.S. Pat. No. 7,768,083 entitled“Arrangements for an Integrated Sensor,” which is assigned to theAssignee of the subject application.

It will be appreciated by those of ordinary skill in the art that whilethe active surface 14 a of the semiconductor die 14 is described hereinas the surface “in” which the magnetic field sensing element is disposedor formed as is the case with certain types of magnetic field elements(e.g., Hall plate), the element may be disposed “over” or “on” theactive semiconductor surface (e.g. magnetoresistance elements). Forsimplicity of explanation however, while the embodiments describedherein may utilize any suitable type of magnetic field sensing elements,such elements will be described generally herein as being formed ordisposed “in” the active semiconductor surface.

In use, the magnetic field sensor 10 like the other sensor embodimentsdescribed herein may be positioned in proximity to a moveablemagnetically permeable ferromagnetic article, or target, such as theillustrated gear 12, such that the magnetic field transducer 22 isadjacent to the article 12 and is thereby exposed to a magnetic fieldaltered by movement of the article. The magnetic field transducer 22generates a magnetic field signal proportional to the magnetic field.

While the magnetic field sensor 10 in FIG. 1 is oriented relative to thetarget 12 such that the transducer 22 is closer to the target than theferromagnetic mold material 30, it will be appreciated that it may bedesirable in certain applications to rotate the sensor 10 by 180° sothat the ferromagnetic mold material is closer to the target than thetransducer. Also, the sensor 10 may be rotated by 90° so that the majorface of the transducer is orthogonal to the target, thereby achieving adifferent type of magnetically sensitive sensor, as may be desirablewhen the transducer is a magnetoresistance element for example.

The ferromagnetic article 12 may be comprised of a hard ferromagnetic,or simply hard magnetic material (i.e., a permanent magnet such as asegmented ring magnet), a soft ferromagnetic material, or even anelectromagnet and embodiments described herein may be used inconjunction with any such article arrangement.

In embodiments in which the article 12 is comprised of a softferromagnetic material, the ferromagnetic mold material 30 is comprisedof a hard ferromagnetic material to form a bias magnet; whereas inembodiments in which the article 12 is comprised of a hard ferromagneticmaterial, the ferromagnetic mold material 30 may be soft ferromagneticmaterial to form a concentrator, or a hard magnetic material where abias field is desired (for example, in the case of a magnetoresistanceelement that is biased with a hard magnetic material or permanentmagnet). In embodiments in which the ferromagnetic mold material 30comprises a hard ferromagnetic material to form a bias magnet and inwhich the sensor 10 is oriented relative to the target such thattransducer 22 is closer to the target than the ferromagnetic moldmaterial 30 as shown, the bias magnet may be referred to as a back biasmagnet.

The magnetic field sensor 10 generally includes additional circuitryformed in the active surface 14 a of the die 14 for processing themagnetic field signal provided by the transducer 22. The lead frame 18includes leads 24 a-24 c for coupling the circuitry to system components(not shown), such as a power source or microcontroller. Electricalconnection between the leads 24 a-24 c and the semiconductor die 14 canbe provided with wire bonds 26 a-26 c, respectively as shown. While thesensor 10 is shown to include three leads 24 a-24 c, it will beappreciated by those of ordinary skill in the art that various numbersof leads are possible. Other techniques for electrically coupling thelead frame leads to the sensor components include solder bumps or balls(FIG. 6) or pillar bumps.

The integrated circuit sensor 10 may be provided in the form of a two tosix pin Single In-Line (SIP) package, or some other number of pins asappropriate. The die attach area 16 on the first surface 18 a of a leadframe 18 is generally a dedicated area of the conductive lead frame toaccept the semiconductor die 14. The die attach area 16 is sometimesreferred to as a die attach paddle or a die attach pad and in someembodiments the die attach pad may be a silver plated or a NiPdAu areafor example. Alternatively, as described in a co-pending U.S. patentapplication Ser. No. 13/350,970 entitled “Methods and Apparatus for aMagnetic Sensor having a Non-conductive Die Paddle” which was filed onJan. 16, 2012 and assigned to the Assignee of the subject application,it may be desirable to form the die attach area with a non-conductivematerial, particularly in applications where Eddy currents can occur.Conventional techniques for securing the die 14 to the die attach area16 include the use of adhesives, such as epoxy or an adhesive tape. Itwill be appreciated by those of ordinary skill in the art that the dieattach area may or may not be a contiguous area. For example, in theembodiment of FIG. 17, the die attach area spans a plurality of leads.

The non-conductive mold material 20 is comprised of a non-conductivematerial so as to electrically isolate and mechanically protect the die14 and the enclosed portion of the lead frame 18. Suitable materials forthe non-conductive mold material 20 include thermoset and thermoplasticmold compounds and other commercially available IC mold compounds. Itwill be appreciated that the non-conductive mold material 20 can containa ferromagnetic material, such as in the form of ferromagneticparticles, as long as such material is non-conductive.

The non-conductive mold material 20 is applied to the lead frame/diesubassembly, such as in a first molding step (FIG. 8), to enclose thedie 14 and a portion of the lead frame 18. The non-conductive moldmaterial 20 has a first surface 20 a and a second, opposing surface 20b. The shape and dimensions of the non-conductive mold material areselected to suit a particular IC package.

In some embodiments as noted above, the ferromagnetic mold material 30is comprised of a hard or permanent magnetic material to form a biasmagnet. As will be apparent to those of ordinary skill in the art,various materials are suitable for providing the ferromagnetic moldmaterial 30 depending on the operating temperature range and finalpackage size. In some embodiments, it may be desirable for theferromagnetic mold material to have a coercivity larger than itsremanence.

Illustrative hard magnetic materials for the ferromagnetic mold materialinclude, but are not limited to hard magnetic ferrites, SmCo alloys,NdFeB alloy materials, or Plastiform® materials of Arnold MagneticTechnologies Corp., or other plastic compounds with hard magneticparticles, for example a thermoset polymer such as polyphenylene sulfidematerial (PPS) or nylon material containing SmCo, NdFeB, or hardferromagnetic ferrite magnetic particles; or a thermoset polymer such asSUMIKON®EME of Sumitomo Bakelite Co., Ltd or similar type of thermosetmold material containing hard magnetic particles. In some embodiments itmay be desirable to align the hard ferromagnetic particles duringmolding to form a more isotropic or directional permanent magneticmaterial by molding in the presence of a magnetic field; whereas, inother embodiments, a sufficient magnet may result without an alignmentstep during molding for isotropic materials. It will be appreciated thata NdFeB or a SmCo alloy may contain other elements to improvetemperature performance, magnetic coercivity, or other magneticproperties useful to a magnetic design.

In other embodiments, the ferromagnetic mold material 30 is comprised ofa soft ferromagnetic material to form a concentrator. As will beapparent to those of ordinary skill in the art, various materials aresuitable for providing the ferromagnetic mold material 30 in the form ofa soft ferromagnetic material. In some embodiments, it may be desirablefor the soft ferromagnetic mold material to have a relatively lowcoercivity and high permeability. Suitable soft ferromagnetic materialsinclude, but are not limited to permalloy, NiCo alloys, NiFe alloys,steel, nickel, and soft magnetic ferrites.

The ferromagnetic mold material 30 is secured to the non-conductive moldmaterial 20, such as in a second molding step (FIG. 8). Theferromagnetic mold material contacts the second surface 20 b of thenon-conductive mold material and also a portion of the sides of thenon-conductive mold material between the first and second surfaces 20 a,20 b, as shown. It will be appreciated that while a molding process isdescribed in FIGS. 8 and 8A as being the process by which theferromagnetic mold material 30 is secured to the non-conductive moldmaterial 20, the ferromagnetic mold material can be (either additionallyor alternatively) secured to the non-conductive mold material 20 usingan adhesive, such as a thermoset adhesive (e.g., a two part epoxy).

In some embodiments, a portion of the non-conductive mold material 20that contacts the ferromagnetic mold material 30 and/or the portion ofthe ferromagnetic mold material that contacts the non-conductive moldmaterial has a securing mechanism in order to improve the adhesionbetween the two materials and to prevent or reduce lateral slippage orshear between the materials. As one example, the lead frame 18 hasextensions 18 c which extend beyond the non-conductive mold material andare enclosed by the ferromagnetic mold material, as shown. Such leadframe extensions additionally enhance the adhesion of the ferromagneticmold material to the lead frame itself. In such embodiments utilizinglead frame portions as a securing mechanism such that the ferromagneticmold material contacts such lead frame portions, it will be appreciatedthat the ferromagnetic mold material should be non-conductive or have asufficiently low conductivity to prevent the leads from electricallyshorting resulting in the device not operating as intended. Alternativeforms of securing mechanisms are shown in other embodiments.

As is shown in FIG. 1B, a portion of the leads 24 a-24 c is enclosed bythe non-conductive mold material 20. The non-conductive mold materialsurrounds the leads out to the edge of the package in order to isolatethe ferromagnetic mold material 30 from the leads (since theferromagnetic mold material may be electrically conductive).

According to the alternative cross-sectional view of FIG. 1C, portionsof the non-conductive mold material 20 adjacent to the leads 24 a-24 cmay be “cut out” around the leads so as to follow the contours of theleads, as shown. This arrangement may be desirable in some applicationsfor magnetic performance reasons, to thereby increase the amount of thehard ferromagnetic material of the ferromagnetic mold material inproximity to the transducer 22. Also shown in FIG. 1C is an alternativesecuring mechanism in the form of lead frame tabs 18 c′. The tabs 18 c′may be planar and may have an eye as shown. With this arrangement, theferromagnetic mold material 30 flows through the eye of the tabs andaround the tabs to improve the adhesion of the ferromagnetic moldmaterial to the lead frame and non-conductive mold material.

It will be appreciated by those of ordinary skill in the art, thatvarious types of processes may be used to form the mold materialsincluding but not limited to molding, such as compression molding,injection molding, and transfer molding, and potting. Furthermore,combinations of the various techniques for forming the mold materialsare possible.

A mold cavity used to define the ferromagnetic mold material 30 mayinclude a mandrel so that the ferromagnetic mold material forms aring-shaped structure having a central aperture 40, here extending fromthe second surface 20 b of the non-conductive mold material to a secondend 30 b of the ferromagnetic mold material. The mold material 30 mayform a conventional O-shaped ring structure or a D-shaped structure.Alternatively, the ferromagnetic mold material 30 may form only apartial ring-like structure, as may be described as a “C” or “U” shapedstructure. More generally, the ferromagnetic mold material 30 comprisesa non-contiguous central region such that the central region is notformed integrally with its outer region. Such central region may be anopen area, such as in the case of aperture 40 in FIG. 1, or may containa ferromagnetic material such as in the embodiment of FIG. 2 forexample.

The ferromagnetic mold material 30 is tapered from its first end 30 a(or a location close to its first end) to its second end 30 b as isapparent from the side view of FIG. 1. In particular, the ferromagneticmold material has a first taper to its outer circumferential surface 32a and a second taper to its inner central aperture surface 32 b. Thepurpose of the taper is to facilitate removal of the sensor 10 from themold cavity. The angle of the taper of the surfaces 32 a, 32 b may bethe same or similar to each other and generally, the angle of the taperof the surfaces 32 a, 32 b is less than approximately 15 to 20 degrees.In some embodiments, the angle of taper is on the order of 2-7 degrees.

As can be seen from the views of FIGS. 1B and 1C, the packaged magneticfield sensor 10 may have a truncated edge 42 for ease of assembly, forexample to facilitate bending the leads and to help mechanically locatethe sensor 10 relative to other structures, such as a circuit board orhousing which holds the sensor, in use. In this case, the ferromagneticmold material 30 may be more accurately described as a D-ring structureor magnet.

Referring also to FIG. 2, an alternative magnetic field sensor 50, inwhich like elements to FIG. 1 are labeled with like referencecharacters, includes semiconductor die 14, a magnetic field sensingelement 22, lead frame 18, non-conductive mold material 20, andferromagnetic mold material 30. The sensor 50 differs from the sensor 10(FIG. 1) in the addition of a third mold material 54 in the centralregion of the ferromagnetic mold material 30.

The third mold material 54 may be formed by a third molding step (FIG.8) or other suitable fabrication technique so as to be secured to theferromagnetic mold material 30. The third mold material 54 may becomprised of a hard ferromagnetic material, a soft ferromagneticmaterial, or a non-ferromagnetic mold compound.

In one embodiment, the ferromagnetic mold material 30 is comprised of ahard ferromagnetic material and the third mold material 54 is comprisedof a soft ferromagnetic material and provides a concentrator magnetizedsuch that two poles are adjacent to the second surface 20 b of thenon-conductive mold material. As described in the above-referenced U.S.Pat. No. 5,781,005, the near presence of opposite poles with respect tothe magnetic field transducer 22 serves to short out the lines of fluxwhen no ferromagnetic target is present, thereby lowering the baselineof the flux density map regardless of airgap, and enhancing the abilityto discern a target present from a target absent condition.

The sensor 50 includes an alternative securing mechanism between thefirst, ferromagnetic and third mold materials, here in the form orridges 18 c″. Other examples of securing mechanisms include the use ofan adhesive material and/or various other features designed to provideinterference and/or an interlocking mechanism between the moldmaterials.

Referring also to FIG. 2A, an alternative magnetic field sensor 56, inwhich like elements to FIG. 2 are labeled with like referencecharacters, includes semiconductor die 14, magnetic field sensingelement 22, lead frame 18, non-conductive mold material 20,ferromagnetic mold material 30, and third mold material 54 in thecentral region of the ferromagnetic mold material. The sensor 56 differsfrom the sensor 50 of FIG. 2 in that here, the sensor is arranged in alead on chip configuration with the lead frame 18 positioned above thedie 14. An adhesive 58 may be used to secure the lead frame 18 to theactive surface 14 a of the die. Here leads 24 a and 24 b areelectrically coupled to the die 14 by respective wire bonds 26 a, 26 b.

Referring to FIG. 3, a further alternative magnetic field sensor 60includes a semiconductor die 62 having a first active surface 62 a inwhich a magnetic field sensing element 64 is disposed and a second,opposing surface 62 b attached to a die attach area 66 on a firstsurface 70 a of a lead frame 70, a non-conductive mold material 74enclosing the die and at least a portion of the lead frame, and aferromagnetic mold material 80 secured to a portion of thenon-conductive mold material. A securing mechanism, such as barbs 18 cof FIG. 1, tabs 18 c′ of FIG. 1C, ridges 18 c″ of FIG. 2 or othersuitable mechanisms, may be provided to enhance the adhesion between thenon-conductive and ferromagnetic mold materials.

The ferromagnetic mold material 80 comprises a ferromagnetic materialand is tapered from a first end 80 a proximate to the lead frame 70 to asecond end 80 b distal from the lead frame. The active die surface 62 ais opposite the die surface 62 b which is attached to the die attacharea 66 and thus, this configuration may be referred to as a “die up”arrangement.

The ferromagnetic mold material 80 is tapered along both its outercircumferential surface 82 a and its inner surface 82 b from its firstend 80 a to its second end 80 b. Here again, the angle of taper of thesurface 82 a may be on the order of less than 15-20 degrees. The angleof the taper of the inner surface 82 b may be the same as or similar tothe angle of the taper of the outer surface 82 a.

The non-conductive mold material 74 has a protrusion 76 extending awayfrom a second surface 70 b of the lead frame 70 as shown. The protrusion76 prevents there being a void in the bottom surface of the sensor 60(adjacent to the second end 80 b of the ferromagnetic mold material),since the presence of a void may make overmolding (described below) moredifficult. It will be appreciated by those of ordinary skill in the artthat the protrusion may extend all or only part of the way to the secondend 80 b of the ferromagnetic mold material (see also FIG. 3A).

The ferromagnetic mold material 80 has a non-contiguous central region,here in the form of a central aperture defined by the innercircumferential surface 80 a and resulting in a ring, or O-shaped magnet80. Here again however, it will be appreciated that the non-contiguouscentral region of the ferromagnetic mold material 80 may take othershapes, so as to form a D-shaped, C-shaped, or U-shaped structure asexamples.

The ferromagnetic mold material 80 may be comprised of a hardferromagnetic material to form a bias magnet. Alternatively, it will beappreciated that the ferromagnetic mold material 80 may be comprised ofa soft ferromagnetic material to thereby form a concentrator.

The sensor 60 may, optionally, include a third mold material 90 in theform of an overmold in order to protect and electrically insulate thedevice. The third mold material 90 may be applied during a third moldingstep (FIGS. 8 and 8A) or alternatively by any suitable fabricationmethod. The overmold 90 is considered optional because its purpose is toprovide electrical insulation and, in embodiments in which theferromagnetic mold material 80 is sufficiently electrically insulative(e.g., provides more than approximately 1 megaohm of resistance incertain applications), the overmold 90 may be eliminated. It will beappreciated that the overmold 90 may be provided for the sensors 10, 50of FIGS. 1-2 and other embodiments.

Suitable materials for providing the overmold material 90 include, butare not limited to standard die encapsulation mold compounds such asPPS, nylon, SUMIKON®EME of Sumitomo Bakelite Co., Ltd., or Hysol® moldcompounds of Henkel AG & Co. KGaA.

Referring also to FIG. 3A, another magnetic field sensor 84 is shownwith like features having like reference characters. As will beapparent, the sensor 84 of FIG. 3A differs from the sensor 60 of FIG. 3only in that the protrusion 86 terminates before the second end 80 b ofthe ferromagnetic mold material 80. Thus, in the embodiment of FIG. 3A,the distal end 86 a of the protrusion is covered with the ferromagneticmold material 80, as shown.

Referring also to FIGS. 4 and 4A, a magnetic field sensor 100 providedin an alternative IC SIP package includes non-conductive andferromagnetic mold materials 104, 108, respectively, and furtherincludes at least one, and here two, integrated passive components suchas resistors, inductors, or capacitors, and here capacitors 102 a, 102b, attached to a lead frame 110. The sensor 100 includes the lead frame110 having a die attach area 112 to which a semiconductor die 116 issecured. A magnetic field sensing element 122 is disposed in an activesurface 116 a of the die 116. Here again, the active die surface 116 ais opposite the die surface 116 b that is secured to the die attach area112 of the lead frame 110. Thus, this arrangement may be referred to asa “die up” arrangement. As will be apparent from comparing the thicknessof the ferromagnetic mold material 108 in FIG. 4A with that in FIGS.1-3, various thicknesses are possible depending on the particularembodiment. As one example, in some embodiments in which theferromagnetic mold material comprises a soft ferromagnetic material toprovide a concentrator, it may be desirable for the ferromagnetic moldmaterial to be somewhat thinner than when the ferromagnetic moldmaterial comprises a hard ferromagnetic material to provide a permanentmagnet. Similarly, various package shapes are possible.

A plurality of leads 120 a-120 h of the lead frame are electricallycoupled to circuitry supported by the die, here with wire bonds 118a-118 d (as shown for leads 120 e-120 h, respectively). The capacitors102 a, 102 b may be useful to reduce EMC, ESD or address otherelectrical issues with the sensor 100. For example, with capacitors 102a, 102 b, power to the sensor may be held longer in order to prevent apower on reset state by holding an output state in the case of a brokenor damaged wire. It is also possible to have other numbers ofcapacitors, for example one capacitor may be provided between a powerand ground or output and ground pins.

The lead frame 110 may have a cutout, depressed, or recessed region 114(FIG. 4A) in which the capacitors 102 a, 102 b can be positioned below asurface 110 a of the lead frame on which the die 116 is positioned. Withthe capacitors positioned below the lead frame surface 110 a, the“active area depth” of the sensor and the entire package thickness isadvantageously reduced as compared to a package having a capacitormounted on the lead frame surface 110 a. The active area depth refers tothe distance from the magnetic field transducer 122 to the “top” surface104 a of the non-conductive mold material. Additional aspects of thesensor 100 including integrated capacitors are described in a U.S.Patent Application Publication No. US-2008-0013298-A1, entitled “Methodsand Apparatus for Passive Attachment of Components for IntegratedCircuits,” which is assigned to the Assignee of the subject application.

The non-conductive mold material 104 and the ferromagnetic mold material108 may be the same as, or similar to the non-conductive andferromagnetic mold materials discussed above in connection with FIGS.1-3. The non-conductive mold material 104 encloses the semiconductor die116, at least a portion of the lead frame 110, and the capacitors 102 a,102 b. The ferromagnetic mold material 108 is secured to a portion ofthe non-conductive mold material 104 and a securing mechanism may beprovided between the non-conductive and ferromagnetic mold materials toenhance adhesion.

The ferromagnetic mold material 108 is comprised of a ferromagneticmaterial. Here again, the ferromagnetic material comprising theferromagnetic mold material 108 may be a soft ferromagnetic material ofthe type described above, in which case the ferromagnetic mold materialforms a concentrator. Alternatively, the ferromagnetic materialcomprising the ferromagnetic mold material 108 may be a hardferromagnetic material of the type described above, in which case theferromagnetic mold material forms for example a bias magnet.

Referring also to FIGS. 5 and 5A, a magnetic field sensor 130 having afurther alternative IC package includes non-conductive and ferromagneticmold materials 134, 138, respectively, and further includes at leastone, and here three, integrated passive components, here capacitors 132a, 132 b, and 132 c. The sensor 130 includes a lead frame 140 having adie attach area 148 on a first surface 140 a to receive a semiconductordie 146 and a second, opposing surface 140 b. A magnetic sensing element136 is disposed in an active surface 146 a of the die 146. Here again,the active surface 146 a of the die 146 is opposite the die surface 146b that is secured to the die attach area. Thus, this arrangement may bereferred to as a “die up” arrangement.

A plurality of leads 142 a-142 f of the lead frame, here in the form ofsurface mount leads, are electrically coupled to circuitry supported bythe die, here with wire bonds 144 a-144 d (as shown for leads 142 c-142f, respectively). Capacitors 132 a-132 c are attached to the lead frame140 on the second surface 140 b of the lead frame opposite the surface146 a on which the die attach area 148 is located, as shown in thecross-section of FIG. 5A for capacitor 132 b. With the capacitorspositioned below the lead frame 140 in this fashion, the active areadepth and the entire thickness of the package is advantageously reducedas compared to a package having a capacitor mounted on the “top” surface140 a of the lead frame. Additional aspects of the sensor 130 includingintegrated capacitors are described in a U.S. Patent ApplicationPublication No. US-2008-0013298-A1 entitled “Methods and Apparatus forPassive Attachment of Components for Integrated Circuits,” which isassigned to the Assignee of the subject application.

The non-conductive mold material 134 and the ferromagnetic mold material138 may be the same as, or similar to the non-conductive andferromagnetic mold materials discussed above in connection with FIGS.1-3. The non-conductive mold material 134 encloses the semiconductor die146, at least a portion of the lead frame 140, and the capacitor 132a-132 c. The ferromagnetic mold material 138 is secured to a portion ofthe non-conductive mold material 134 and a securing mechanism may beprovided between the non-conductive and ferromagnetic mold materials toenhance adhesion.

The ferromagnetic mold material 138 is comprised of a ferromagneticmaterial. Here again, the ferromagnetic material comprising theferromagnetic mold material 138 may be a soft ferromagnetic material ofthe type described above, in which case the ferromagnetic mold materialforms a concentrator or magnetic flux guide. Alternatively, theferromagnetic material comprising the ferromagnetic mold material 138may be a hard ferromagnetic material of the type described above, inwhich case the ferromagnetic mold material forms a bias magnet.

Referring also to FIG. 5B, an alternative cross-sectional view of thesensor 130 is shown in which the shape of the non-conductive andferromagnetic mold materials 134, 138 is tailored to follow the contourof the surface 140 b of the lead frame and the capacitor 132 b. Moreparticularly, the non-conductive mold material 134 encloses the magneticfield sensor die 146, a portion of the lead frame 140, and the capacitor132 b and has a reduced thickness adjacent to the surface 140 b of thelead frame as shown. With this arrangement, the ferromagnetic moldmaterial 138 is closer to the semiconductor die 146 than in thecross-sectional view of FIG. 5A. Close proximity between theferromagnetic mold material 138 and the magnetic field sensing element136 enhances the effectiveness of the concentrator and/or bias magnetprovided by the ferromagnetic mold material.

Referring to FIG. 6, a magnetic field sensor 150, as may provide acurrent sensor, includes non-conductive and ferromagnetic mold materials174, 178, respectively, and further includes at least one integratedcomponent, here a capacitor 172. The sensor 150 includes a lead frame156 having a first surface 156 a and a second, opposing surface 156 b.The lead frame 156 includes a plurality of leads 152 a-152 h and acurrent conductor portion 154. Here, the capacitor 172 is secured to thelead frame 156 on the “bottom” (with respect to the view of FIG. 6)surface 156 b of the lead frame.

The sensor 150 also includes a semiconductor die 166 having a firstsurface 166 a and a second, opposing surface 166 b. The die 166 has amagnetic field sensing element 158 disposed in the first surface 166 a.The die 166 is disposed on the lead frame 156 so that the magnetic fieldsensing element 158 is in close proximity to the current conductorportion 154. The die 166 has an orientation that is upside down (i.e.,the first surface 166 a is directed downward) in relation to theconventional orientation with which a die is mounted in an integratedcircuit package and may be referred to as a “flip-chip” configuration.

Solder balls 160 a-160 c on the first surface 166 a are coupled directlyto the leads 152 e-152 h as shown. An insulator 164 separates the die166 from the lead frame 156. The insulator 164 can be provided in avariety of ways. For example, in one embodiment, a first portion of theinsulator 164 includes a layer of a BCB resin material depositeddirectly on the first surface 166 a of the die 166. A second portion ofthe insulator 164 may include a layer of underfill material or a tapematerial including but not limited to a polymer tape such as a Kapton®tape, deposited on the lead frame 156.

With this small outline integrated circuit (SOIC) package arrangement,the Hall effect element 158 is disposed in close proximity to thecurrent conductor portion 154 and at a predetermined position relativeto the conductor portion 154, such that a magnetic field generated by anelectrical current passing though the current conductor portion 154, isin a direction substantially aligned with a maximum response axis of themagnetic field sensing element 158. Additional aspects of the sensor 150are described in a U.S. Patent Application Publication No.US2008/0297138, entitled “Current Sensor,” which is assigned to theAssignee of the subject application.

While three solder balls 160 a-160 c are shown, any number of solderballs can be provided, including dummy solder balls for stabilizing thedie 166. Also, while solder balls 160 a-160 c are shown, otherconnection methods can also be used, including, but not limited to goldbumps, eutectic or high lead solder bumps, no-lead solder bumps, goldstud bumps, polymeric conductive bumps, anisotropic conductive paste, orconductive film.

The non-conductive mold material 174 and the ferromagnetic mold material178 may be the same as, or similar to the non-conductive andferromagnetic mold materials discussed above in connection with FIGS.1-3. Thus, the non-conductive mold material 174 encloses the magneticfield sensor die 166, at least a portion of the lead frame 152, and thecapacitor 172. The ferromagnetic mold material 178 is secured to aportion of the non-conductive mold material 174 and a securing mechanismmay be provided between the non-conductive and ferromagnetic moldmaterials to enhance adhesion.

The ferromagnetic mold material 178 is comprised of a ferromagneticmaterial. Here again, the ferromagnetic material comprising theferromagnetic mold material 178 may be a soft ferromagnetic material ofthe type described above, in which case the ferromagnetic mold materialforms a concentrator or magnetic flux shield. In operation, the fluxconcentrator 178 tends to concentrate the magnetic flux generated by thecurrent passing through the current conductor portion 154 so as to causethe current sensor 150 to have a higher sensitivity than otherwisepossible. The flux concentrator 178 will also tend to guide small fieldsaway from the magnetic sensor element in certain configurations andtherefore shield the sensor from externally applied stray fields.Alternatively, the ferromagnetic material comprising the ferromagneticmold material 178 may be a hard ferromagnetic material of the typedescribed above, in which case the ferromagnetic mold material forms abias magnet.

Referring to FIG. 7, another alternative magnetic field sensor 180includes a semiconductor die 182 having a first surface 182 a in which aplurality of magnetic field sensing elements 184 a-184 b are disposedand a second, opposing surface 182 b attached to a die attach area 186on a first surface 188 a of a lead frame 188, a non-conductive moldmaterial 190 enclosing the die and at least a portion of the lead frame,and a ferromagnetic mold material 194 secured to a portion of thenon-conductive mold material. As is apparent, the magnetic field sensingelements 184 a-184 b are here shown to be disposed “on” the first diesurface 182 a in the manner of a magnetoresistance element. However, asnoted above, it will be appreciated that this and the other embodimentsdescribed herein may utilize any magnetic field sensing device type.

The non-conductive mold material 190 and the ferromagnetic mold material194 may be the same as, or similar to the non-conductive andferromagnetic mold materials discussed above in connection with FIGS.1-3. The ferromagnetic mold material 194 is comprised of a ferromagneticmaterial. Here again, the ferromagnetic material comprising theferromagnetic mold material 194 may be a soft ferromagnetic material ofthe type described above, in which case the ferromagnetic mold materialforms a concentrator. Alternatively, the ferromagnetic materialcomprising the ferromagnetic mold material 194 may be a hardferromagnetic material of the type described above, in which case theferromagnetic mold material forms a bias magnet.

The ferromagnetic mold material 194 contacts several surfaces of thenon-conductive mold material 190, including portions of a top surface190 a of the non-conductive mold material, as shown. With thisarrangement of the ferromagnetic mold material 194 being adjacent to themagnetic field sensing elements 184 a, 184 b, lower magnetic fields maybe achieved than in embodiments in which the ferromagnetic mold materialdoes not extend over the top surface 190 a of the non-conductive moldmaterial (e.g., FIGS. 1-3), as may be particularly desirable inembodiments in which the magnetic field sensing elements are GMRelements. Furthermore, providing the ferromagnetic mold material over aportion of the top surface 190 a may also operate as a form of securingmechanism, to thereby improve the adhesion between the non-conductiveand ferromagnetic mold materials.

Referring to FIG. 8, a flow diagram shows an illustrative process forfabricating the sensors of FIGS. 1-7. In a step 200, the lead frame(e.g., lead frame 18 of FIG. 1) is formed. Various materials andprocesses may be used to form the lead frame. As an example, the leadframe may be a stamped or etched metal, such as copper or a copperalloy.

In step 204, the semiconductor die (e.g., die 14 of FIG. 1) is attachedto the lead frame. For example, the die may be attached to the dieattach area (e.g., die attach area 16 of FIG. 1) by a conventionaltechnique such as by soldering or with the use of an epoxy (eitherconductive or non-conductive epoxy may be used depending on the need) oran adhesive tape. Alternatively, in the case of a flip-chip arrangement,the die may be attached to the lead frame with solder balls for example.

In an optional step 206, an integrated component (e.g., capacitors 102a-102 b of FIG. 4) is provided on the lead frame. The capacitors may beattached via a solder process or a conductive epoxy process onto thelead frame. Furthermore, step 206 may be combined with step 204 suchthat a single solder reflow or epoxy cure heat cycle may be used tosecure the die to the die attach area and also secure the capacitor tothe lead frame.

In a further optional step 208, circuitry supported by the dieincluding, but not limited to the magnetic field sensing element, iselectrically coupled to leads of the lead frame, such as by wirebonding. Step 208 is optional because in certain configurations, such asthe flip-chip configuration of FIG. 6, attaching the die to the leadframe in step 204 includes coupling the circuitry to the leads, such aswith the use of the solder bumps.

The non-conductive mold material is formed in steps 212 and 216 in whichthe die/lead frame subassembly is placed in a mold cavity into which thenon-conductive mold material is introduced, such as by injectionmolding, compression molding, transfer molding or potting.

In step 218, the subassembly, now including the non-conductive moldmaterial, is removed (optionally following a time interval appropriatefor curing, depending on the composition of the non-conductive moldmaterial) from the first mold cavity and placed in a second mold cavity.In step 222, the ferromagnetic mold material is introduced into thesecond mold cavity to form a bias magnet or concentrator.

As noted above, in some embodiments, the ferromagnetic mold material canbe secured to the non-conductive mold material using an adhesive, suchas a thermoset adhesive (e.g., a two part epoxy). According to one suchexample, prior to step 222 (for example between steps 218 and 222), theepoxy is applied to the bottom surface 20 b and lower side portions ofthe non-conductive mold material 20 (FIG. 1) and the epoxy cures as aresult of the heat applied during the molding of the ferromagnetic moldmaterial in step 222.

If the sensor is to include a third mold material (e.g., third moldmaterial 54 of FIG. 2 or overmold material 90 of FIG. 3), then in step226 (optionally following a time interval appropriate for curing,depending on the third or overmold material), the subassembly includingthe non-conductive and ferromagnetic mold materials, is removed from thesecond mold cavity and placed into a third mold cavity and in step 228,the third mold or overmold material is introduced into the third moldcavity. It will be appreciated by those of ordinary skill in the artthat the use of additional mold materials is possible. In step 230, thesubassembly is removed from the final mold cavity (i.e., the second moldcavity in embodiments in which a third mold is not used, or the thirdmold cavity in embodiments in which such is used).

Referring also to FIG. 8A, a flow diagram shows an alternative processfor fabricating the sensors of FIGS. 1-7. In a step 232, the lead frameis formed. In step 234, the lead frame is placed in a mold cavity. Instep 236, the ferromagnetic mold material (e.g., mold material 30 ofFIG. 1) is introduced into the mold cavity to form a magnet orconcentrator.

In step 238, the subassembly including the lead frame and ferromagneticmold material is removed from the mold cavity and the semiconductor dieis attached to the lead frame die attach area, such as by soldering orwith the use of an epoxy or an adhesive tape. In optional step 240, anintegrated component, such as capacitors 102 a-102 b of FIG. 4, isattached to the lead frame. Here again steps 238 and 240 may be combinedsuch that a single solder reflow or epoxy cure may be used to secure thedie to the die attach area and also secure the capacitor to the leadframe.

In a further optional step 242, circuitry supported by the die includingis electrically coupled to leads of the lead frame, such as by wirebonding. Step 242 is optional because in certain configurations, such asthe flip-chip configuration of FIG. 6, attaching the die to the leadframe in step 238 includes coupling the circuitry to the leads, such aswith the use of the solder bumps.

The non-conductive mold material (such as mold material 20 of FIG. 1) isformed in step 244 in which the die/lead frame subassembly is placedinto a mold cavity into which the non-conductive mold material isintroduced, such as by injection molding, compression molding, transfermolding or potting.

In embodiments in which the sensor includes a third mold material (e.g.,third mold material 54 of FIG. 2 or overmold material 90 of FIG. 3),then in step 246 (optionally following a time interval appropriate forcuring, depending on the third or overmold material), the subassemblyincluding the non-conductive and ferromagnetic mold materials, isremoved from the second mold cavity and placed into a third mold cavityand in step 248, the third mold or overmold material is introduced intothe third mold cavity. In step 249, the subassembly is removed from thefinal mold cavity (i.e., second or third mold cavity depending onwhether optional steps 246, 248 are performed).

The mold steps of the fabrication processes described in connection withFIGS. 8 and 8A may be achieved by the same or different mold processes.For example, all of the molding steps 216, 222, and 230 may be achievedby the same molding process, such as transfer molding. Alternatively,one or more such steps may be by transfer molding and the other suchsteps may be by injection molding. Thus, it will also be appreciated bythose of ordinary skill in the art that the different mold steps may beby the same or different molding processes and therefore at the same ordifferent speeds and/or pressures for example. In general, the moldsetup and cure times can be selected based on the mold process (e.g.,taking into account molding pressure, speed, and temperature), moldmaterials and mold geometry.

In some applications transfer molding is desirable because of therelatively lower pressures and thinner mold cavity requirements (ascompared to injection molding for example). As a result the lowerpressures, transfer molding generally can result in lower stress on thesensor and the ability to use thinner mold cavities can increase thethroughput per mold shot, thereby reducing the cost of fabrication.

Referring also to FIG. 9, according to a further aspect, a bias magnetor concentrator can be provided by a layer 254 of ferromagnetic materialformed over a first surface 250 a of a semiconductor wafer 250. Variousconventional wafer level packaging techniques may be used to provide thelayer 254, such as pouring, molding, or coating. The magnetic fieldsensor embodiments of FIGS. 10-13 are formed from wafer 250. Inembodiments in which the layer 254 provides a bias magnet, the layer iscomprised of a material containing hard magnetic material particles,such as a hard ferrite, a NdFeB alloy, a SmCo alloy, a NdFeB alloy, athermoplastic polymer with hard magnetic particles, or a thermosetpolymer with hard magnetic particles. And in embodiments in which thelayer 254 provides a concentrator, the layer is comprised of a softferromagnetic material, such as NiFe, Ni, a Ni alloy, steel, or ferrite.

The thickness of the ferromagnetic layer 254 may be tailored for aparticular application and particular sensor characteristics, includingbut not limited to the sensitivity of the magnetic field sensing elementand the airgap. Illustrative thicknesses for layer 254 are on the orderof 100 to 500 microns.

Referring also to FIG. 10, a magnetic field sensor 260 includes amagnetic field sensing element 262 disposed in a first surface 264 a ofthe die 264 and a ferromagnetic material layer 266 formed over a second,opposing surface 264 b of the die 264. The die 264 and layer 266 may beprovided by dicing the wafer 250 (FIG. 9) into individual IC device die.A lead frame 268 includes leads 268 a, 268 b and a die attach area (notvisible in the view of FIG. 10) to which the second surface 264 b of thedie is attached. Portions of the lead frame 268 (not shown in FIG. 10for clarity) may extend to support the die in the manner of other leadframe embodiments. The sensing element 262 and other circuitry supportedby the first surface 264 a of the die may be coupled to the leads byvarious techniques, such as wire bonds as shown. The die/lead framesubassembly may be overmolded with an overmold material 270 as shown toprovide a packaged magnetic field sensor device 260.

Referring also to FIG. 11, a further alternative magnetic field sensor300 as may be formed by separating the wafer 250 of FIG. 9 intoindividual IC device die is shown. The sensor 300 includes a magneticfield sensing element 304 disposed in a first surface 308 a of the die308 and a ferromagnetic material layer 310 formed over the second,opposing surface 308 b of the die 308. Solder balls 312 are providedover the first surface 308 a of the die for coupling the magnetic fieldsensing element 304 and associated circuitry to a lead frame (notshown), such as in a flip-chip arrangement similar to the arrangementshown in FIG. 6. Thus the lead frame may be the same as or similar tothe lead frame of FIG. 6.

Referring also to FIG. 12, another alternative magnetic field sensor320, that also may be formed by separating the semiconductor wafer 250of FIG. 9 into individual die, includes a magnetic field sensing element324 disposed in a first surface 328 a of the die 328 and a ferromagneticmaterial layer 330 formed over the second, opposing surface 328 b of thedie 308.

Solder balls 334 are formed for coupling the magnetic field sensingelement 324 and associated circuitry to a lead frame, such as any of theabove-described lead frames, a Printed Circuit Board (PCB), or othersubstrate with die or components, such as may take the form of aMulti-Chip Module (MCM) for example. While the solder balls 334 may beformed over the ferromagnetic layer 330, here, regions of the layer 330are opened, such as by laser ablation, to permit the solder balls tocontact the die 328, as shown. Through Silicon Vias (TSVs) 338 areformed through the die 328 to couple the magnetic field sensing element324 and associated circuitry to the solder balls 334, as shown, forfurther coupling to a lead frame. The TSVs may be formed prior toapplication of the ferromagnetic material 330 to the wafer to isolatethe ferromagnetic materials from the wafer fabrication process andreduce potential cross-contamination of the TSV tool.

Another magnetic field sensor embodiment 340, that may be formed bydicing the semiconductor wafer 250 of FIG. 9 into individual die, isshown in FIG. 13 to include a semiconductor die 344 having a firstsurface 344 a over which the layer 346 of ferromagnetic material isformed and a second opposing surface 344 b. A magnetic field sensingelement 348 (shown as a Hall sensor in the substrate or epi layer) andassociated circuitry (not shown) are disposed in the first surface 344 aof the die. TSVs 350 are formed through the die 344 to couple themagnetic field sensing element 348 to solder balls 352, as shown, forfurther coupling to a lead frame that may be the same as or similar toany of the above-described lead frames. An optional layer 354 may beprovided between the die surface 344 a and the layer 346 in order toprotect the die from particles in the layer 346. In such embodiments,the layer 354 may comprise, but is not limited to, a polyimide or BCBlayer deposited at the wafer level, or a tape layer or other insulator.

Referring also to FIG. 14, an illustrative process for fabricating thesensors 260, 300, 320, 340 of FIGS. 10-13, respectively, is shown. Instep 370, one or more magnetic field sensing elements and associatedcircuitry are formed in the first, active surface of the wafer. Inembodiments in which the magnetic field sensor and other circuitryformed in a first surface of the die are coupled to a lead frame orother structure from a second, opposing surface of the die, TSVs areformed through the wafer and solder balls (e.g., solder balls 334 ofFIG. 12) are formed on or applied to the wafer in step 370.

In step 374, a layer of ferromagnetic material, such as layer 310 ofFIG. 11, is formed over a surface of a semiconductor wafer by any ofvarious wafer level packaging techniques, such as by pouring, molding,or coating.

A lead frame may be formed in an optional step 378. Various materialsand processes may be used to form the lead frame. As an example, thelead frame may be a stamped or etched metal, such as copper, a copperalloy, or in some instances a soft magnetic material such as Kovar™.

In optional step 386, the die and the magnetic field sensing element andassociated circuitry are attached to the lead frame. The die/lead framesubassembly is placed into a mold cavity in optional step 390, and anovermold material is introduced into the mold cavity to enclose the dieand a portion of the lead frame in optional step 394. Steps 378-394 areconsidered optional since, as mentioned above in connection with FIG. 13for example, in some embodiments, the die may be attached to a PCB, MCM,or other structure, without the use of a lead frame.

Another magnetic field sensor embodiment 400 is shown in FIG. 15 toinclude a semiconductor die 402 having a first, active surface 402 a inwhich a magnetic field sensing element 404 is formed and a second,opposing surface 402 b. A lead frame 406 having leads 406 a-406 c isprovided with a die attach area 406 d to which the surface 402 b of thedie 402 is attached, such as with the use of adhesives, such as epoxy oran adhesive tape.

A bias magnet 410 is provided with a non-contiguous central region 410a. As in the above-described embodiments, the bias magnet 410 may takethe form of a ring-shaped structure in which case the non-contiguouscentral region is an aperture or alternatively may form only a partialor alternative ring-shaped structure, such as a D-shaped structure, aC-shaped structure, or a U-shaped structure.

The magnet 410 includes one or more channels 410 b extending laterallyfrom the central region 410 a. The die/lead frame/magnet subassembly isovermolded with an overmold material 412 to enclose the die, magnet, anda portion of the lead frame. Here, the magnet channel 410 b is providedfor the purpose of facilitating the overmolding step as will bedescribed.

The bias magnet 410 may be formed by a molding process, such asinjection molding or transfer molding, as described above in the case ofthe ferromagnetic mold material in the various embodiments. In thiscase, the magnet 410 may be molded to the lead frame 406 (e.g., in themanner described above in connection with FIG. 8A). Alternatively, themagnet 410 may be a separately molded structure or may be a sinteredmagnet and may be attached to the lead frame with an epoxy or anadhesive tape.

Referring also to FIG. 16, an illustrative process for fabricating themagnetic field sensor 400 of FIG. 15 is shown. The lead frame 406 isformed in step 420 by any conventional method. In step 424, one or moremagnetic field sensing elements and associated processing circuitry areformed in the first surface 402 a of a semiconductor die 402. In step428, the bias magnet 410 having a non-contiguous central region 410 aand one or more laterally extending channels 410 b is formed. Inembodiments in which the magnet 410 is formed by a molding process, themold cavity can be provided with structures to form the one or morechannels in the ferromagnetic mold material. The magnet 410 is attachedto the lead frame, such as with the use of epoxy or an adhesive tape, instep 432. In embodiments in which the magnet 410 is molded to the leadframe, steps 428 and 432 may be combined.

In step 436, the die/lead frame subassembly is placed into a mold cavityfor overmolding with an overmold material 412 (FIG. 15) in step 440. Instep 444, the device 400 is evacuated through the one or more channels410 b. For example, air may be removed from the central region 410 awith a vacuum system (not shown) coupled to the channel(s) 410 b. Itwill also be appreciated that use of one or more channels to permitevacuation of the non-contiguous central region can be applied to theabove-described embodiments. For example, in step 222 of FIG. 8, thesecond mold cavity can have one or more structures sized and arranged sothat the second mold material is formed so as to have one or morechannels.

Referring also to FIG. 17, an alternative magnetic field sensor 450,includes a semiconductor die 452, a magnetic field sensing element 462,a lead frame 454, a non-conductive mold material 456, and aferromagnetic mold material 458. The sensor may include a third,overmold material, not shown here, but described above in otherembodiments, which may increase the size of the package beyond 458. Thenon-conductive mold material 456 and the ferromagnetic mold material 458may be the same as or similar to like materials discussed above inconnection with other embodiments. The sensor 450 further includesintegrated passive components, here in the form of capacitors 464 a, 464b, attached to lead frame portions 454 a, 454 b, and 454 c whichterminate in corresponding leads, as shown. Here again, thenon-conductive mold material 456 encloses the die 452, at least aportion of the lead frame 454, and the capacitors 464 a, 464 b.

Here, the die 452 is attached to the top of the lead frame 454. Anadhesive may be used to secure the die to the lead frame 454 and moreparticularly to lead frame portions 454 a, 454 b, and 454 c. Thus, inthis embodiment, since the die attach area of the lead frame 454 extendsacross multiple leads 454 a-454 c, the adhesive attaching the die to thelead frame must be comprised of a non-conductive material, such as anon-conductive epoxy, or a die attach tape such as a Kapton® tape. Here,leads 454 a-454 c are electrically coupled to the die 452 by wire bonds480. The sensor 450 may be fabricated according to the above-describedillustrative processes, such as are shown in FIGS. 8 and 8A.

The sensor 450 includes two securing mechanisms. The first securingmechanism is provided in the form of slots 484 in the lead frame thatserve to enhance adhesion of the non-conductive mold material 456 to thelead frame 454. A second securing mechanism, in the form of overhangingportions 486 of the lead frame that extend beyond the non-conductivemold material, serve to enhance adhesion of the non-conductive moldmaterial 456 to the ferromagnetic mold material 458 and the lead frame.As noted above in conjunction with FIG. 1, because the overhangingportions 486 of the lead frame extend into the ferromagnetic moldmaterial, it will be appreciated that the ferromagnetic mold materialshould be non-conductive or have a sufficiently low conductivity toprevent the leads from electrically shorting resulting in the device notoperating as intended.

Referring to FIG. 18, in which like elements to FIG. 1 are labeled withlike reference characters, an alternative magnetic field sensor 500 of aform similar to the sensor 10 of FIG. 1 includes semiconductor die 14having a first, active surface 14 a in which a magnetic field sensingelement or transducer 22 is formed and a second, opposing surface 14 battached to a die attach area 16 on a first surface 18 a of a lead frame18, a non-conductive mold material 20 enclosing the die and at least aportion of the lead frame, and a ferromagnetic mold material 30 securedto the non-conductive mold material.

As in the sensor 10 of FIG. 1, the ferromagnetic mold material 30 of thesensor 500 has a central aperture 40 extending from the second surface20 b of the non-conductive mold material 20 to a second end 30 b of theferromagnetic mold material 30. Also in the same manner as sensor 10,the ferromagnetic mold material 30 of sensor 500 is tapered from itsfirst end 30 a (or a location close to its first end) to its second end30 b. In particular, the ferromagnetic mold material has a first taperto its outer circumferential surface 32 a and a second taper to itsinner central aperture surface 32 b′.

The sensor 500 differs from the sensor 10 (FIG. 1) in that the taper ofthe inner central aperture surface 32 b′ has multiple slopes rather thana single slope. The surface 32 b′ may have a first sloped portion 504and a second sloped portion 508 as shown. It will be appreciated thatwith regard to the taper of surfaces 32 a and 32 b′, the particularangle of the respective taper and whether the respective taper has asingle slope or multiple sloped portions can be the same or differentand can be selected to suit a particular sensor/fabrication. Althoughthe surface 32 b′ is shown in FIG. 18 to have two sloped portions, itwill be appreciated that more than two slopes are possible.

Referring to FIG. 19, in which like elements to FIG. 1 are labeled withlike reference characters, an alternative magnetic field sensor 510 of aform similar to the sensor 10 of FIG. 1 includes semiconductor die 14having a first, active surface 14 a in which a magnetic field sensingelement or transducer 22 is formed and a second, opposing surface 14 battached to a die attach area 16 on a first surface 18 a of a lead frame18, a non-conductive mold material 20 enclosing the die and at least aportion of the lead frame, and a ferromagnetic mold material 30 securedto the non-conductive mold material.

As in the sensor 10 of FIG. 1, the ferromagnetic mold material 30 of thesensor 500 has a non-contiguous central region, here labeled 512,extending from the second surface 20 b of the non-conductive moldmaterial 20 to a second end 30 b of the ferromagnetic mold material 30.

The sensor 510 differs from the sensor 10 (FIG. 1) in that a separatelyformed element 514 is disposed in and secured to the central region 512of the ferromagnetic mold material 30. This arrangement is in contrastto the open area central aperture 40 shown in FIG. 1 and also incontrast to the arrangement of FIG. 2 in which the central region of themold material 30 contains a third mold material 54.

More particularly, the separately formed element 514 is not formed by amolding step in conjunction with other elements of the sensor 510. Theelement 514 may be a machined or sintered element or it may be aseparately molded part, as examples.

The element 514 may be secured to the region 512 of the mold material 30by various techniques. For example, the element 514 may be secured tothe surface 32 b of the mold material 30 with an adhesive or with apress fit arrangement. As another example, the separately formed element514 may be placed in a mold cavity into which the mold material 30 isinjected for example, in which case the element may be secured to themold material 30 with interfering features, such as barbs extending fromthe element. As yet another example, the material 30 could be pottedwith a potting material that may be filled with a ferromagneticmaterial. It will be appreciated by those of ordinary skill in the artthat while the illustrated element 514 has a taper complementary to thetaper of the region 512 of the mold material 30, in some embodiments theelement 514 and/or the region 512 may not be tapered, or tapered withdifferent or multiple slopes.

The element 514 may be comprised of a hard ferromagnetic material, asoft ferromagnetic material, or a non-ferromagnetic, non-conductivematerial. As one example, the separately formed element 514 may becomprised of a potting compound filled with a soft ferromagneticmaterial, such as a soft ferrite. As another example, the separatelyformed element 514 may be a sintered steel rod sized and shaped to fitin the region 512. In assembly, the element 514 may be positioned in theregion 512 and secured to the surface 32 b of the mold material 30 withan adhesive. Alternatively, the mold material 30 may be molded aroundthe steel rod element 514.

Referring to FIG. 20, in which like elements to FIG. 4 are labeled withlike reference characters, an alternative magnetic field sensor 520 of aform similar to the sensor 100 of FIG. 4 includes non-conductive andferromagnetic mold materials 104, 108, respectively, and furtherincludes at least one, and here two, integrated passive components suchas resistors, inductors, or capacitors, and here capacitors 102 a, 102b, attached to a lead frame 524. The lead frame 524 has a die attacharea to which a semiconductor die 116 is secured. A magnetic fieldsensing element 122 is disposed in an active surface of the die 116.

The sensor 520 differs from the sensor 100 of FIG. 4 in that the leadframe 524 contains one or more slots, and here three slots 524 a, 524 b,and 524 c. As is well known in the art, in the presence of a changing ACor transient magnetic field (e.g., a magnetic field surrounding acurrent carrying conductor), eddy currents can be induced in theconductive lead frame 524. The presence of the slots can move theposition of the eddy currents and also the influence of the eddycurrents to result in a smaller magnetic field error so that a Halleffect element experiences a smaller magnetic field from the eddycurrents than it would otherwise experience, resulting in a less errorin the measured field. Furthermore, if the magnetic field associatedwith the eddy current is not uniform or symmetrical about the Halleffect element, the Hall effect element might generate an undesirableoffset voltage.

Lead frame slots 524 a, 524 b, and 524 c tend to reduce a size (e.g., adiameter or path length) of the closed loops and the position of theloops with respect to the sensing element(s) in which the eddy currentstravel in the lead frame 524. It will be understood that the reducedsize of the closed loops in which the eddy currents travel results insmaller eddy currents for a smaller local affect on the changingmagnetic field that induced the eddy current. Therefore, the measuredmagnetic field of a sensor having a Hall effect 122 element is lessaffected by eddy currents due to the slots 524 a-524 c.

Instead of an eddy current rotating about the Hall effect element 122,the slot(s) 524 a-524 c result in eddy currents to each side of the Hallelement. While the magnetic fields resulting from the eddy currents areadditive, the overall magnitude field strength, compared to a singleeddy current with no slot, is lower due to the increased distance of theeddy currents to the sensing element(s). While three slots 524 a-c areshown, the eddy current influence on the Hall effect element 122 wouldbe reduced by only having the slot 524 c under the sensing element 122.

It is understood that any number of slots can be formed in a widevariety of configurations to meet the needs of a particular application.In the illustrative embodiment of FIG. 20, first, second and third slots524 a, 524 b, and 524 c are formed in the lead frame 524 in relation toa Hall effect element 122 centrally located in the die. The slots reducethe eddy current flows and enhance the overall performance of thesensor.

It is understood that the term slot should be broadly construed to covergenerally interruptions in the conductivity of the lead frame. Forexample, slots can include a few relatively large holes as well assmaller holes in a relatively high density. In addition, the term slotis not intended to refer to any particular geometry. For example, slotincludes a wide variety of regular and irregular shapes, such as tapers,ovals, etc. Further, it is understood that the direction of the slot(s)can vary. Also, it will be apparent that it may be desirable to positionthe slot(s) based upon the type of sensor.

The slotted lead frame 524 can be formed from a metal layer of suitableconductive materials including but not limited to, for example, copper,copper alloys, aluminum, copper, titanium, tungsten, chromium, Kovar™and/or nickel or alloys of the metals. Additional details of the slottedlead frame 524 may be found in U.S. Patent Application Publication No.US-2012-0086090-A1 for example, which application is assigned to theassignee of the subject invention and incorporated herein by referencein its entirety.

The sensor 520 further differs from the sensor 100 of FIG. 4 in that atleast one lead of the lead frame has a passive component coupled inseries, or “in-line”. To this end, a lead otherwise formed by continuousor coupled leads or lead portions 120 a and 120 e is split or broken andthe portions coupled by one or more passive component 106. Moreparticularly, each of the lead portions 120 a and 120 e has an end thatis spaced from and proximate to the end of the other lead. Passivecomponent 106 is coupled to both the lead portion 120 a and to leadportion 120 e, thereby being electrically connected in series with thelead. This arrangement can advantageously permit series coupling ofpassive components with one or more leads.

The passive component 106 may take various forms, such as a resistor,capacitor, or inductor as examples, which component(s) is provided forvarious purposes, such as to improve EMC performance. In an embodimentthe element 106 is a resistor. Also, it will be appreciated that whileonly one lead is shown to have an in-line passive component 106, thesame or a different type of passive component can be similarly coupledin line with more than one lead. Also, a single lead, such as thatformed by lead portions 120 a and 120 e, can have more than one breakand more than one passive component coupled across the respective breaksso as to form an arrangement in which more than one passive component iscoupled in series with a respective lead.

Referring to FIG. 21, in which like elements to FIG. 1 are labeled withlike reference characters, an alternative magnetic field sensor 540 of aform similar to the sensor 10 of FIG. 1 includes semiconductor die 14having a first, active surface 14 a in which a magnetic field sensingelement or transducer 22 is formed and a second, opposing surface 14 battached to a die attach area on a first surface of a lead frame 18, anon-conductive, typically non-ferromagnetic, mold material 20 enclosingthe die and at least a portion of the lead frame, and a ferromagneticmold material 30 secured to the non-conductive mold material.

Referring also to the top view of the sensor 540 in FIG. 21A, lead frame18 has a plurality of leads 24 a, 24 b, and 24 c. While three leads 24a-24 c are shown, it will be appreciated that various numbers of leadsare possible, such as between two and eight leads.

According to an aspect of the invention, the sensor 540 contains asuppression device 544. The suppression device 544 is provided in orderto enhance the electromagnetic compatibility (EMC) of the sensor 540 andto reduce electrostatic discharge (ESD). To this end, the suppressiondevice 544 comprises a ferromagnetic material.

The suppression device 544 may be provided in various geometries (i.e.,size and shape), at various locations of the sensor, and may befabricated by various techniques, including molding. Most generally, thesuppression device 544 is integral with the sensor 540.

The molded ferromagnetic suppression device 544 is positioned to enclosea portion of one or more leads at a location on the respective lead(s)spaced from the non-conductive mold material 20. The particular locationof the suppression device 544 along the length of the lead can bereadily varied and may be a function of whether the leads will be bentfor assembly for example.

The suppression device 544 comprises a ferromagnetic mold material, thatmay be the same as or similar to the ferromagnetic mold material 30. Dueto the placement of suppression device 544 on the leads, the moldmaterial comprising the device 544 must be of sufficient resistivity toprevent unwanted electrical signals from being passed between the leads.The molded ferromagnetic suppression device 544 may be comprised of ahard or permanent magnetic material. In some embodiments it may bedesirable to align hard ferromagnetic particles during molding to form amore anisotropic or directional magnetic material by molding in thepresence of a magnetic field; whereas, in other embodiments, asufficient ferromagnetic material may result without an alignment stepduring molding for isotropic materials. It will be appreciated that aNdFeB or a SmCo alloy may contain other elements to improve temperatureperformance, magnetic coercivity, or other magnetic properties useful toa magnetic design.

In other embodiments, the suppression device 544 is comprised of a softferromagnetic material. In some embodiments, it may be desirable for themolded soft ferromagnetic element 544 to have a relatively lowcoercivity and high permeability. Suitable soft ferromagnetic materialsinclude, but are not limited to permalloy, NiCo alloys, NiFe alloys,steel, nickel, and soft ferromagnetic ferrites. As described above forhard ferromagnetic materials, it may also be desirable to form a softferromagnetic suppression device 544 in the presence of a magnetic fieldfor a more anisotropic ferromagnetic material. In another embodiment itmay be desirable to form an isotropic soft ferromagnetic suppressionbody without using a magnetic field applied during molding.

The molded suppression device 544 may be formed at the same time andwith the same fabrication technique as the ferromagnetic mold material30, such as in step 222 of FIG. 8 or in step 236 of FIG. 8A for example,in which case such process steps additionally serve to form the moldedferromagnetic suppression device so as to enclose a portion of at leastone lead. Alternatively, the molded suppression device 544 may be formedat a different time and/or with a different fabrication technique as theferromagnetic mold material 30.

The suppression device 544 extends from the lead 24 a in a firstdirection (e.g., above the lead) by a height “a” and extends from thelead 24 a in a second direction (e.g., below the lead) by a height “b”.Here, the heights a and b are shown to be approximately the same;however, it will be appreciated that this need not be the case. Thus,the overall height of the suppression device 544 is a+b, additionallyplus the thickness of the lead. This overall height of the suppressiondevice may be (but is not required to be) less than the overall heightof the non-conductive mold material 20 (given by heights c+d,additionally plus the thickness of the lead), so that the suppressiondevice does not extend beyond the main package body defined by moldmaterial 20 alone or in combination with mold material 30.

Referring also to the top view of FIG. 21A, the suppression device 544may comprise a plurality of individual molded ferromagnetic devices 544a, 544 b, 544 c, each enclosing a portion of a respective lead 24 a, 24b, and 24 c and each having a width “e” selected to ensure a nominalspacing between adjacent devices and/or leads. Alternatively, and asshown in the alternative top view of FIG. 21B, the suppression device544 may be provided in the form of a shared molded device formed toenclose a portion of more than one lead, and here all three leads 24 a,24 b, and 24 c. It will be appreciated by those of ordinary skill in theart that in embodiments in which the suppression device 544 encloses aportion of more than one lead, the mold material comprising the device544 is a non-conductive or high resistivity ferrite type of soft or hardferromagnetic material or other high resistivity ferromagnetic material.Furthermore, it will be appreciated that a combination of individualmolded ferromagnetic devices enclosing a portion of a single respectivelead and shared molded ferromagnetic devices enclosing a portion of morethan one lead is also possible.

Referring also to FIG. 22, in which like elements to FIG. 1 are labeledwith like reference characters, an alternative magnetic field sensor 550of a form similar to the sensor 10 of FIG. 1 includes semiconductor die14 having a first, active surface 14 a in which a magnetic field sensingelement or transducer 22 is formed and a second, opposing surface 14 battached to a die attach area on a first surface of a lead frame 18, anon-conductive mold material 20 enclosing the die and at least a portionof the lead frame, and a ferromagnetic mold material 30 secured to thenon-conductive mold material. The lead frame 18 has a plurality of leads(represented in FIG. 22 by illustrative lead 24) and the sensor 540contains an alternative molded ferromagnetic suppression device 554.

Suppression device 554 comprises a first mold element 558 and a secondmold element 560. The first mold element 558 encloses a portion of atleast one lead and the second mold element 560 encloses at least aportion of the first mold element.

The first mold element 558 may be the same as or similar to thenon-conductive mold material 20 and thus, may comprise thermoset andthermoplastic mold compounds and other commercially available IC moldcompounds. It will be appreciated that the first mold element 558 cancontain a ferromagnetic material, such as in the form of ferromagneticparticles, as long as such material is non-conductive. The second moldelement 560 of the suppression device 554 may be the same as or similarto the ferromagnetic mold material 30 as discussed above or may becomprised of a soft ferromagnetic material. And a third mold element mayalso be provided.

The first and second mold elements 558, 560 may be fabricated by thesame or different techniques and at the same or a different time as thenon-conductive and ferromagnetic mold materials 20, 30, respectively,and as each other. In one embodiment, the first mold element 558 isformed by transfer molding at the same time as the non-conductive moldmaterial 20 (e.g., in step 216 of FIG. 8 or in step 244 of FIG. 8A) andthe second mold element 560 is formed by injection molding at the sametime as the ferromagnetic mold material 30 (e.g., in step 222 of FIG. 8or in step 236 of FIG. 8A). Benefits of using the first, non-conductivemold element 558 may include eliminating any electrical performancedegradation or changes that may result from the second, ferromagneticmold element 560 contacting the lead and/or reducing stress on the leaddue to the fabrication technique by which the ferromagnetic mold element560 is formed (e.g., injection molding).

While the second mold element 560 is shown to be spaced from and not incontact with the lead 24, it will be appreciated by those of ordinaryskill in the art that in certain embodiments, it may be desirable toallow the second mold element to contact the lead. In fact, if thesecond mold element 560 is sufficiently non-conductive, so as not toundesirably alter the electrical performance of the lead, then thesecond molded element can enclose the first mold element 558 and thuscontact the lead.

The suppression device 554 extends from the lead 24 in a first direction(e.g., above) by a height f+a (the height of the first and second moldelements, respectively) and extends from the lead 24 in a seconddirection (e.g., below) by a height g+b (the height of the first andsecond mold elements, respectively). Here, the heights a and b are shownto be approximately the same as each other and the heights f and g areshown to be approximately the same as each other; however, it will beappreciated that this need not be the case. In other words, the firstand/or second mold element can extend in one direction from the leadmore than in another direction. Also, in the illustrated embodiment,while the thickness of the first mold element 558 is shown to beapproximately the same as the thickness of the second mold element, thisneed not be the case.

The overall height of the suppression device 554 (i.e., a+b+f+g,additionally plus the thickness of the lead) may be (but is not requiredto be) less than the overall height of main package body defined by theheight of the mold material 20 in combination with the height of themold material 30.

Referring to FIG. 23 and according to a further aspect of the invention,a magnetic field sensor 570 is provided with a molded ferromagneticsuppression device 572 enclosing a passive component 576. The sensor 570is of a form similar to the sensor 10 of FIG. 1, in which like elementsare labeled with like reference characters, and includes semiconductordie 14 having a first, active surface 14 a in which a magnetic fieldsensing element or transducer 22 is formed and a second, opposingsurface 14 b attached to a die attach area on a first surface of a leadframe 18, a non-conductive mold material 20 enclosing the die and atleast a portion of the lead frame, and a ferromagnetic mold material 30secured to the non-conductive mold material.

As is known and described in the above-referenced U.S. PatentApplication Publication No. US-2012-0086090-A1, it is sometimesdesirable to integrate one or more passive components, such ascapacitors, resistors, inductors, on an integrated circuit lead framefor filtering and/or other functionality. The passive component 576,such as a surface mount capacitor, may be fabricated by techniquesdescribed in the above-referenced U.S. Patent Application PublicationNo. US-2012-0086090-A1.

The suppression device 572 may comprise a ferromagnetic mold materialthat is the same as or similar to the ferromagnetic mold material 30 andthat may be formed at the same or at a different time than theferromagnetic mold material 30 and/or by the same or a differentfabrication technique. In one embodiment, the molded ferromagneticsuppression device 572 is formed by an injection molding process at thesame time that the ferromagnetic mold material 30 is formed. The moldmaterial comprising the device 572 must be of sufficient resistivity toprevent unwanted electrical signals from being passed between the leads.

In another embodiment, the element 572 may be made of the same materialand at the same time as the non-conductive mold material 20. Thepressure of molding is generally lower for transfer molding compared toinjection molding and therefore the lower pressure of the moldingprocess during molding of the non-conductive mold material 20 at thesame time as suppression device 572 may be desirable for reliability ofthe attachment of the passive component 576 to the lead frame 24.

The molded device 572 is sized and shaped to enclose the passivecomponent(s) 576, as shown. The suppression device 572 extends from thelead 24 a in a first direction (e.g., above) by a height “a” and extendsfrom the lead 24 a in a second direction (e.g., below) by a height “b”.Here, the heights a and b are shown to be somewhat different, with theheight a being greater than the height b to enclose the passivecomponent 576; however, it will be appreciated that the heights a and bmay be substantially the same as long as the height a is sufficient toenclose the passive component. The overall height of the suppressiondevice 572 of a+b, additionally plus the thickness of the lead, may be(but is not required to be) less than the overall height of thenon-conductive mold material 20 (given by heights c+d, additionally plusthe thickness of the lead), so that the suppression device 572 does notextend beyond the main package body defined by mold material 20 alone orin combination with mold material 30. The passive element 576 is shownon the same side of the lead frame as the die 14, but in anotherembodiment the capacitor could be on the opposite side of the leadframe. In such an embodiment the distance a may be smaller than thedistance b shown in FIG. 23 from the lead frame.

Referring also to the top view of sensor 570 in FIG. 23A, in theillustrative embodiment, leads 24 a, 24 b, and 24 c have extendedregions 28 to facilitate coupling one or more passive components 576,578 between respective pairs of leads, as shown, such as by soldering orconductive adhesive or conductive epoxy. Alternatively, and as shown inthe alternative top view of FIG. 23B, the extended regions 28 of theleads may be omitted and the passive component(s) may be coupleddirectly across respective pair(s) of leads, as shown. The arrangementof FIG. 23B can result in a smaller molded ferromagnetic suppressiondevice 572 because the passive components 576 and 578 are not offsetfrom each other as in the embodiment of FIG. 23A. More particularly, inthe arrangement of FIG. 23B, the passive components 576 and 578 arepositioned across respective pairs of leads 24 a, 24 b and 24 b, 24 c inparallel with one another, thereby enabling the width “W” of the moldedelement 572 to be smaller than the like dimension of the molded element572 shown in FIG. 23A. It will be appreciated by those of ordinary skillin the art that while the suppression device 572 here encloses passivedevices 576 and 578; alternatively, the device may comprise multiplemolded devices, each of which encloses one or more respective passivecomponent(s) and lead portion(s).

Referring to FIG. 24, in which like elements to FIG. 1 are labeled withlike reference characters, an alternative magnetic field sensor 590 of aform similar to the sensor 10 of FIG. 1 includes semiconductor die 14having a first, active surface 14 a in which a magnetic field sensingelement or transducer 22 is formed and a second, opposing surface 14 battached to a die attach area on a first surface of a lead frame 18, anon-conductive mold material 20 enclosing the die and at least a portionof the lead frame, and a ferromagnetic mold material 30 secured to thenon-conductive mold material. The lead frame 18 includes a plurality ofleads (represented in FIG. 24 by illustrative lead 24 a) and the sensor590 contains an alternative molded ferromagnetic suppression device 594.

The suppression device 594 encloses one or more passive components, hererepresented by capacitor 576, as well as one or more mold elements, herea first mold element 596 and a second mold element 598. The first moldelement 596 encloses at least one passive component 576 and a portion ofthe leads to which the passive component is coupled and the second moldelement 598 encloses at least a portion of the first mold element.

The first mold element 596, like the mold element 558 of FIG. 22, maycomprise a non-conductive material that may be the same as or similar tothe non-conductive mold material 20 and thus, may comprise thermoset andthermoplastic mold compounds and other commercially available IC moldcompounds. It will be appreciated that the first mold element 596 cancontain a ferromagnetic material, such as in the form of ferromagneticparticles, as long as such material is sufficiently non-conductive. Thesecond mold element 598 of the suppression device 594, like mold element560 of FIG. 22, may be the same as or similar to the ferromagnetic moldmaterial 30 as discussed above.

In another embodiment, element 598 may be formed during a third moldingprocess to allow a soft ferromagnetic material to be used for 598 whenelement 30 is made of a hard ferromagnetic material and body 20 is madeof a non-conductive material, which is either ferromagnetic or notferromagnetic.

The first and second mold elements 596, 598 may be fabricated by thesame or different techniques and at the same or a different time thanthe non-conductive and ferromagnetic mold materials 20, 30,respectively, and as each other. In one embodiment, the first moldelement 596 is formed by transfer molding at the same time as thenon-conductive mold material 20 (e.g., in step 216 of FIG. 8 or in step244 of FIG. 8A) and the second mold element 598 is formed by injectionmolding at the same time as the ferromagnetic mold material 30 (e.g., instep 222 of FIG. 8 or in step 236 of FIG. 8A). Benefits of using thefirst, non-conductive mold element 596 may include eliminating anyelectrical performance degradation or changes that may result from thesecond, ferromagnetic mold element 598 contacting the lead and/orreducing stress on the lead due to the fabrication technique by whichthe ferromagnetic mold element 598 is formed (e.g., injection molding).

In the case where a third mold is used to form element 598, the thirdmold material may be of a soft ferromagnetic mold material and formed ata different time than the injection mold of element 30. This third moldstep does not have to be third in sequence as it could occur after themolding of non-conductive mold material 20 but before the molding offerromagnetic mold material 30. Although in many cases the third moldmaterial would be a soft ferromagnetic material, in other embodimentsthis third mold material may be a hard ferromagnetic material as well.

While the second mold element 598 is shown to be spaced from and not incontact with the lead 24, it will be appreciated by those of ordinaryskill in the art that in certain embodiments, it may be desirable toallow the second mold element to contact the lead. In fact, if thesecond mold element 598 is sufficiently non-conductive, so as not toundesirably alter the electrical performance of the lead, then thesecond molded element can enclose the first mold element 596 and thuscontact the lead.

The suppression device 594 extends from the lead 24 a in a firstdirection (e.g., above) by a height f+a (the height of the first andsecond mold elements, respectively) and extends from the lead 24 in asecond direction (e.g., below) by a height g+b (the height of the firstand second mold elements, respectively). Here, the heights a and b areshown to be approximately the same as each other and the heights f and gare shown to be approximately the same as each other; however, it willbe appreciated that this need not be the case. The height a is selectedto enclose the passive component 576. Also, in the illustratedembodiment, while the thickness of the first mold element 596 is shownto be approximately the same as the thickness of the second moldelement, this need not be the case.

The overall height of the suppression device 594, a+b+f+g, additionallyplus the thickness of the lead, may be (but is not required to be) lessthan the overall height of the main package body defined by the heightmold material 20 in combination with the height of the mold material 30.

Referring to FIG. 25, in which like elements to FIG. 1 are labeled withlike reference characters, an alternative magnetic field sensor 600 of aform similar to the sensor 10 of FIG. 1 includes semiconductor die 14having a first, active surface 14 a in which a magnetic field sensingelement or transducer 22 is formed and a second, opposing surface 14 battached to a die attach area on a first surface of a lead frame 18, anon-conductive mold material 20 enclosing the die and at least a portionof the lead frame, and a ferromagnetic mold material 30 secured to thenon-conductive mold material. The lead frame 18 has a plurality of leads(represented in FIG. 25 by illustrative lead 24) and the sensor 600contains an alternative suppression device 604.

Suppression device 604 is provided in the form of a ferromagnetic beadthat is inserted over or around the lead 24 during manufacture, prior tofabrication of the non-conductive mold material 20 so that the bead isenclosed by the non-conductive mold material, as shown.

The bead 604 has a central aperture that is sized to fit over the lead24. The bead may be deformable and have a central aperture dimensionselected to result in a slight compression fit with respect to the lead.With this arrangement, during manufacture, the bead can be slipped ontothe lead 24 and slid or pushed along the length of the lead to alocation close to the die 14. The compression fit results in the leadremaining in place at the location close to the die in order tofacilitate molding of the non-conductive mold material 20 over a portionof the lead frame, the die, and the bead.

The bead may be sphere or tubular shaped as examples and may besymmetrical with respect to its central aperture so as to have asubstantially circular cross-section or alternatively, the bead may beoffset with respect to its central aperture and may have an alternativecross-section, such as an oval or rectangular cross-section.

The overall diameter of the suppression device 604 is selected toprovide desired EMC and EMI performance, as a function of the sensortype and application and the ferromagnetic material comprising the bead.Suitable materials for the ferromagnetic bead include but are notlimited to soft ferrite materials.

Referring to FIG. 26, in which like elements to FIG. 1 are labeled withlike reference characters, an alternative magnetic field sensor 620 of aform similar to the sensor 10 of FIG. 1 includes semiconductor die 14having a first, active surface 14 a in which a magnetic field sensingelement or transducer 22 is formed and a second, opposing surface 14 battached to a die attach area on a first surface of a lead frame 18, anon-conductive mold material 20 enclosing the die and at least a portionof the lead frame, and a ferromagnetic mold material 30 secured to thenon-conductive mold material. Referring also to the top view of thesensor 620 in FIG. 26A, lead frame has a plurality of leads 24 a, 24 b,and 24 c and the sensor 620 contains an alternative suppression device624.

Suppression device 624 encloses one or more passive components, such ascapacitor 576, and comprises one or more ferromagnetic beads 628 and amold element 630. The passive component 576 may be the same as orsimilar to the passive component 576 of FIG. 23. The ferromagnetic bead628 may be the same as or similar to the bead 604 of FIG. 25.

The mold element 630 may be the same as or similar to the non-conductivemold material 20 for example. Here however, the mold element 630 issized and shaped to enclose the passive component 576 and bead 628 asshown. Considerations affecting the height and width of the mold element630 can be the same as or similar to considerations discussed above.

The mold element 630 may be fabricated by the same or a differenttechnique and at the same or a different time than the non-conductivemold material 20. As an alternative, the mold element 630 may be thesame as or similar to the ferromagnetic mold material 30, or may be of athird mold material, for example comprising a soft ferromagneticmaterial as described above.

Referring also to the top view of FIG. 26A, leads 24 b and 24 c acrosswhich the passive component 576 is coupled have extended regions 28 tofacilitate securing the component 576 in place, such as by soldering orwith a conductive adhesive or conductive epoxy. The extended regions 28may also be added to leads, on one or both sides of the lead 24 a forexample, without passive components but with a ferromagnetic bead 628 ato allow positioning of the ferromagnetic bead at a predeterminedposition on the lead or leads. The extended regions 28 on leads 24 b and24 c that are used for attachment of the passive component 576 may alsobe used to assist in the placement of the bead 628 b, 628 c along thelength of the respective lead. The sensor 620 is here shown to havethree ferromagnetic beads 628 a, 628 b, and 628 c, each associated withand secured around a respective lead 24 a, 24 b, and 24 c, as shown. Itwill be appreciated by those of ordinary skill in the art however thatmore or fewer beads and passive components may be desirable to suit aparticular sensor type/application. It will also be appreciated that oneor more of the beads 628 a-628 c may be positioned at a differentlocation along the respective lead, such as close to the die 14(provided the extension 28 is not present or does not preventpositioning of the bead closer to the die) so as to be enclosed in themain sensor body 20 (similar to the arrangement in FIG. 25 for example).Furthermore, more than one bead can be secured to the same lead. In anembodiment an adhesive material may be used to secure the bead to a leadprior to the molding step of the mold element 630.

Referring to FIG. 27, in which like elements to FIG. 1 are labeled withlike reference characters, an alternative magnetic field sensor 640 of aform similar to the sensor 10 of FIG. 1 includes semiconductor die 14having a first, active surface 14 a in which a magnetic field sensingelement or transducer 22 is formed and a second, opposing surface 14 battached to a die attach area 16 on a first surface 18 a of a lead frame18, a non-conductive mold material 20 enclosing the die and at least aportion of the lead frame, and a mold material 30 secured to thenon-conductive mold material, here with a securing mechanism in the formof barbs 18 c.

According to an aspect of the invention, the sensor 640 includes aconductive coil 644. Coils are used in magnetic field sensors forvarious reasons, for example to generate a magnetic field for diagnosticor self test functionality as described in a U.S. Patent Application No.2010/00211347, for calibration as is described in a U.S. Pat. No.8,030,918, and for resetting a GMR magnetic field sensing element asdescribed in a U.S. Pat. No. 8,063,634, each of which is assigned to theAssignee of the subject application and incorporated herein by referencein its entirety. In many instances, such conductive coils are formed onthe semiconductor die itself.

The illustrative coil 644 on the other hand is positioned relative tothe magnetic field sensing element 22 to function as a back bias magnet,so as to provide a magnetic field which can be used to detect movementof a proximate target. To this end, the coil 644 is positioned adjacentto the second surface 20 b of the non-conductive mold material 20 sothat the transducer 22 is closer to the target 12 than the coil 644, asshown. Here again, it will be appreciated that it may be desirable incertain applications to rotate the sensor 640 by 180° so that the coil644 is closer to the target than the transducer or to rotate the sensorby 90° so that the major face of the transducer is orthogonal to thetarget, thereby achieving a different type of magnetically sensitivesensor, as may be desirable when the transducer is a magnetoresistanceelement for example which has a different axis of sensing elementsensitivity than a planar Hall element. It may also be desirable in anembodiment to rotate coil 644 such that its central axis is parallel tothe surface of the die 14 for certain sensor configurations and sensingelement combinations.

Various techniques and materials can be used to form the coil 644. Forexample, the coil can be formed from copper wire of various sizes andwith various automated processes so as to provide an insulator betweencoil windings. The coil material selection, wire gauge selection, numberof turns, and other design choices can be readily varied to suit aparticular application so as to produce a magnetic field of a desiredstrength. The coil 644 may be formed so that each turn is in the shapeof a circle, rectangle, or other shapes such as an oval, as desirable tosuit a particular application and packaging arrangement.

The coil 644 may be secured to the second surface 20 b of thenon-conductive mold material 20 by various means. As one example, anadhesive, such as an epoxy, may be used to secure the coil in place.Once secured in place, the mold material 30 may be formed in the mannerdescribed above, such as by injection molding for example. Moreparticularly, in accordance with the illustrative process of FIG. 8 forexample, step 218 may be modified such that after the subassembly,comprising the die and lead frame, is removed from the mold cavity, thecoil 644 is attached to the mold material surface 20 b before thesubassembly is moved to the second mold cavity for formation of the moldmaterial 30. With this arrangement, the mold material 30 can flow intothe center of the coil, as shown.

In operation, a bias current is applied to the coil 644 which causes abias magnetic field to be generated. The transducer 22 is responsive toperturbations in the magnetic field caused by movement of the target 12.It will be appreciated by those of ordinary skill in the art that themold material 30 can be provided in the form of a hard ferromagneticmaterial, a soft ferromagnetic material, or even a non-conductivematerial. For example, in embodiments in which the material 30 is a softferromagnetic material, the magnetic field generated by the coil 644 canbe focused or otherwise concentrated as desired by the softferromagnetic mold material 30. Alternatively, in embodiments in whichthe material 30 is a hard ferromagnetic material, the magnetic fieldprovided by the coil 644 can be used to modulate the magnetic fieldprovided by the hard ferromagnetic material 30, in order to therebyreduce the peak current otherwise required to provide the same peakvalue of magnetic field strength when compared to the case of the coilalone (i.e., if the hard ferromagnetic mold material 30 were notpresent). In another embodiment, a separately formed element such aselement 514 of FIG. 19 may be disposed in the central aperture 40.

In some embodiments, since the back bias functionality is provided bythe coil, the mold material 30 may be eliminated entirely (as is shownin FIG. 29) in which case the non-conductive mold material 20 with thecoil 644 attached to its second surface 20 b can be packaged to providethe resulting sensor IC. Such an arrangement can be provided in apackage of the type described in a U.S. Pat. No. 6,265,865 or a U.S.Pat. No. 5,581,179, each of which is assigned to the Assignee of thesubject application and incorporated herein by reference in itsentirety.

Referring also to FIG. 28, in which like elements to FIG. 3A are labeledwith like reference characters, an alternative magnetic field sensor 650of a form similar to the sensor 60 of FIG. 3A includes a semiconductordie 62 having a first active surface 62 a in which a magnetic fieldsensing element 64 is disposed and a second, opposing surface 62 battached to a die attach area 66 on a first surface 70 a of a lead frame70, a non-conductive mold material 74 enclosing the die and at least aportion of the lead frame, and a mold material 80 secured to a portionof the non-conductive mold material.

The non-conductive mold material 74 has a protrusion 86 extending awayfrom a second surface 70 b of the lead frame 70 as shown. As explainedabove, the protrusion 86 prevents there being a void in the bottomsurface of the sensor 650 (adjacent to the second end 80 b of theferromagnetic mold material), since the presence of a void may makeovermolding more difficult. It will be appreciated by those of ordinaryskill in the art that the protrusion may extend all or only part of theway to the second end 80 b of the mold material.

The sensor 650 includes a coil 654 that may the same as or similar tothe coil 644 of FIG. 27. Here, the coil 654 is positioned concentricallywith respect to the protrusion 86 of the non-conductive mold material74, although it will be appreciated that concentric positioning is notrequired. It will be appreciated that the taper to the protrusion 86 maybe eliminated or altered as suitable for a particular application. Hereagain, the coil 654 may be secured to the mold material 74 by anadhesive. Alternatively however, the coil 654 may be sized and shaped toprovide an interference fit with respect to the protrusion 86 such thatadhesive is not necessary and the coil 654 may be sufficiently held inplace relative to the mold material 74 by the interference fit when thesubassembly, including the mold material 74, lead frame 70 and die 62,are placed into the mold cavity for formation of the mold material 80(e.g., in a modified step 218 of FIG. 8 in which the coil is placed overthe protrusion 86 after the subassembly is removed from the first moldcavity and before it is placed into the second mold cavity).

While the sensor 650 is shown to have a protrusion 76 of the type shownin FIG. 3A, which protrusion extending only partially through the moldmaterial 80 to terminate before the second end 80 b of the moldmaterial, it will be appreciated that a similar sensor including a coilthat may be (although is not required to be) concentrically disposedwith respect to a protrusion of the non-conductive mold material can beprovided with a protrusion of the type shown in FIG. 3, which protrusionextends to the second end 80 b of the mold material 80.

In operation, a bias current is applied to the coil 654 which causes abias magnetic field to be generated. The transducer 64 is responsive toperturbations in the magnetic field caused by movement of a target. Itwill be appreciated by those of ordinary skill in the art that the moldmaterial 80 can be provided in the form of a hard ferromagneticmaterial, a soft ferromagnetic material, or even a non-conductivematerial. For example, in embodiments in which the material 80 is a softferromagnetic material, the magnetic field generated by the coil 654 canbe focused or otherwise concentrated as desired by the softferromagnetic mold material 80. Alternatively, in embodiments in whichthe material 80 is a hard ferromagnetic material, the magnetic fieldprovided by the coil can be used to modulate the magnetic field providedby the hard ferromagnetic material 80, in order to thereby reduce thepeak current otherwise required to provide the same magnetic fieldstrength with just the coil (i.e., if the hard ferromagnetic moldmaterial 80 were not present).

Here again, since the back bias functionality is provided by the coil,the mold material 80 may be eliminated entirely (as is shown in FIG. 29)in which case the non-conductive mold material 74 with the coil 654attached to its surface can be packaged to provide the resulting sensorIC. Such an arrangement can be provided in a package of the typedescribed in one of the above-referenced U.S. patents.

In applications including the mold material 80, such mold material maybe tapered from a first end 80 a proximate to the lead frame 70 to asecond end 80 b distal from the lead frame (or for some portion thereof)similarly to the embodiment of FIG. 3A and the sensor 650 may,optionally, include a third mold material 90 in the form of an overmoldin order to protect and electrically insulate the device.

Referring to FIG. 29, in which like elements to FIG. 3A are labeled withlike reference characters, an alternative magnetic field sensor 660 of aform similar to the sensor 60 of FIG. 3A includes a semiconductor die 62having a first active surface 62 a in which a magnetic field sensingelement 64 is disposed and a second, opposing surface 62 b attached to adie attach area 66 on a first surface 70 a of a lead frame 70 and anon-conductive mold material 74 enclosing the die and at least a portionof the lead frame.

The sensor 660 includes a coil 664 that may the same as or similar tothe coil 644 of FIG. 27. The coil 644 is secured to, and moreparticularly, in the embodiment of FIG. 29 is enclosed by, thenon-conductive mold material 74. The wire of the coil 664 may be woundaround a mandrel or bobbin 656, as shown. In one illustrativeembodiment, the mandrel 656 may be comprised of a soft ferromagneticmaterial or a plastic and remain part of the final device. In otherembodiments, the mandrel 656 is used during coil winding but then notmade a part of the final package, for example in the case of FIGS. 27and 28. The mandrel 656 and coil 664 may be secured to the surface 70 bof the lead frame 70 that is opposite the die 62 with an adhesive orother securing mechanism, such that the coil is secured to the leadframe when the subassembly is placed in a mold cavity in step 212 (FIG.8) and the non-conductive mold material 74 is formed in step 216 (FIG.8).

In operation, a bias current is applied to the coil 664 which causes abias magnetic field to be generated and the transducer 64 is responsiveto perturbations in the magnetic field caused by movement of a proximatetarget. While the ferromagnetic mold material (such as mold material 80of FIG. 3A) is eliminated in the sensor 660 of FIG. 29, it will beappreciated by those of ordinary skill in the art that a ferromagneticmold material may be provided as explained in connection with anyforegoing embodiments in order to concentrate the magnetic fieldgenerated by the coil (in the case of a soft ferromagnetic moldmaterial) or to provide a magnetic field for modulation by acoil-generated magnetic field (in the case of a hard ferromagnetic moldmaterial).

Having described preferred embodiments of the invention it will nowbecome apparent to those of ordinary skill in the art that otherembodiments incorporating these concepts may be used.

For example, it will be appreciated by those of ordinary skill in theart that the package types, shapes, and dimensions, including but notlimited to the thicknesses of the mold materials, can be readily variedto suit a particular application both in terms of the electrical andmagnetic requirements as well as any packaging considerations.

It will also be appreciated that the various features shown anddescribed herein in connection with the various embodiments can beselectively combined. As only a few of many examples, the barbs shown inFIG. 1, the channel provided in the bias magnet of FIG. 15, the passivecomponents attached to leads of FIGS. 23-24, and the coil of FIGS. 27-29may be implemented in other embodiments.

Accordingly, it is submitted that that the invention should not belimited to the described embodiments but rather should be limited onlyby the spirit and scope of the appended claims. All publications andreferences cited herein are expressly incorporated herein by referencein their entirety.

What is claimed is:
 1. A magnetic field sensor comprising: a lead framehaving a first surface and a second opposing surface; a semiconductordie having a first surface in which a magnetic field sensing element isdisposed and a second opposing surface attached to the first surface ofthe lead frame; a non-conductive mold material enclosing the die and atleast a portion of the lead frame; and a ferromagnetic mold materialsecured to a portion of the non-conductive mold material, wherein theferromagnetic mold material comprises a central aperture having asurface extending from the non-conductive mold material to an outerperipheral surface of the ferromagnetic mold material, wherein thesurface of the central aperture comprises a bend at an intermediatelocation such that the surface of the central aperture has a first slopefrom the non-conductive mold material to the bend and a second slopedifferent than the first slope from the bend to the outer peripheralsurface of the ferromagnetic mold material.
 2. The magnetic field sensorof claim 1 wherein the ferromagnetic mold material is further secured toand in direct contact with a second portion of the lead frame thatextends beyond the non-conductive mold material and terminates in theferromagnetic mold material.
 3. The magnetic field sensor of claim 1wherein the ferromagnetic mold material is a hard ferromagneticmaterial.
 4. The magnetic field sensor of claim 3 wherein the hardferromagnetic material is selected from the group consisting of aferrite, a SmCo alloy, a NdFeB alloy, a thermoplastic polymer with hardmagnetic particles, and a thermoset polymer with hard magneticparticles.
 5. The magnetic field sensor of claim 1 wherein the leadframe comprises at least one slot.
 6. The magnetic field sensor of claim1 wherein the non-conductive mold material consists of a thermoset orthermoplastic mold compound.
 7. The magnetic field sensor of claim 1further comprising a non-conductive adhesive coupled between the firstsurface of the lead frame and the second surface of the semiconductordie.
 8. The magnetic field sensor of claim 7 wherein the non-conductiveadhesive consists of a non-conductive epoxy or a die attach tape.
 9. Amagnetic field sensor comprising: a lead frame having a first surface, asecond opposing surface, and having at least one slot; a semiconductordie having a first surface in which a magnetic field sensing element isdisposed and a second opposing surface attached to the first surface ofthe lead frame; a non-conductive mold material enclosing the die and atleast a portion of the lead frame; and a ferromagnetic mold materialsecured to a portion of the non-conductive mold material, wherein theferromagnetic mold material comprises an aperture having a surfaceextending from the non-conductive mold material to an outer peripheralsurface of the ferromagnetic mold material, wherein the surface of theaperture comprises a bend such that the surface of the aperture has afirst slope from the non-conductive mold material to the bend and asecond slope different than the first slope from the bend to the outerperipheral surface of the ferromagnetic mold material.
 10. The magneticfield sensor of claim 9 wherein the ferromagnetic mold material isfurther secured to and in direct contact with a second portion of thelead frame that extends beyond the non-conductive mold material andterminates in the ferromagnetic mold material.
 11. The magnetic fieldsensor of claim 9 wherein the non-conductive mold material consists of athermoset or thermoplastic mold compound.
 12. The magnetic field sensorof claim 9 further comprising a non-conductive adhesive coupled betweenthe first surface of the lead frame and the second surface of thesemiconductor die.
 13. The magnetic field sensor of claim 12 wherein thenon-conductive adhesive consists of a non-conductive epoxy or a dieattach tape.
 14. The magnetic field sensor of claim 9 wherein theferromagnetic mold material comprises a hard ferromagnetic material toform a bias magnet.
 15. The magnetic field sensor of claim 14 whereinthe hard ferromagnetic material is selected from the group consisting ofa ferrite, a SmCo alloy, a NdFeB alloy, a thermoplastic polymer withhard magnetic particles, and a thermoset polymer with hard magneticparticles.